Ionic liquid additive for lithium-ion battery

ABSTRACT

An ionic liquid additive for lithium-ion batteryAn ionic liquid for adding to an electrolyte of a lithium-ion battery, the ionic liquid comprises a compound with a dual core structure having the general formula (I):wherein each of cationic group X1 and X2 are heterocyclic aromatic and amine.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional ApplicationNo. 63/139,860, filed Jan. 21, 2021, the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an additive to an electrolyte forlithium-ion battery, in particular but not limited to an ionic liquid asan additive to the electrolyte.

BACKGROUND OF THE INVENTION

In recent years, the demand for batteries with high power, high energydensity and long cyclic stability has increased with the rapiddevelopment of the application of lithium-ion batteries in power batterysystems. Due to the continuous pursuit for high-energy densitybatteries, the use of electrodes with high-areal density andhigh-compaction density is currently one of the common methods in theindustry. However, a resulting problem would be that the diffusion oflithium ions in the electrode becomes unsatisfactory. Furthermore, theinterface impedance between the positive and negative electrodesincreases, leading to greater polarization of the battery on the averagevoltage difference between charging and discharging curves, which makesthe battery performance worse.

During the formation of lithium-ion batteries, a solid electrolyteinterface (SEI) layer is formed on the surface of the anode, whichcontrols the passage of lithium ions. When the formed SEI film is toothick and the impedance is high, lithium ions cannot migrate andpenetrate, it will result in lithium precipitation. When the SEI film isnot sufficiently dense and stable, it will dissolve gradually or mayrupture during the charging and discharging processes, exposing thenegative electrode and permitting its chemical reaction with theelectrolyte. This brings about a continual decrease in the capacity ofbattery as the electrolyte is consumed by reacting with the negativeelectrode.

Another relatively prominent problem with lithium-ion batteries would bethe increase of internal temperature of the battery due to improperheating, overcharging, puncture damage, etc. Puncture damage will resultin short circuit when the positive and negative electrodes are incontact. It may not be possible to suppress the rise in internaltemperature of the battery and this is likely to result in thedecomposition of the SEI film and electrolytes. During thedecomposition, H₂, O₂, HF, PF₅ and other active flammable compounds areproduced. When the temperature rises to 200° C., the decompositionreaction of electrolytes and cathode materials will be occurred. Suchdecomposition reaction generates large amount of hydrogen, oxygen, andfluoride, leading to potential fire and explosion hazards. Theperformance and thermal safety of a lithium-ion battery depends on a lotwhich includes but not exclusively the cathode/anode materials, theproperty of the electrolyte as well as their relationship with the SEIlayer on the surface of electrode.

An ionic liquid is a molten salt composed of anion and cation, whichstill exhibits a liquid state below 100° C. It has low volatility, highmelting point, high ionic conductivity, a wide potential window and is agood flame retardant. With the aforementioned, it is a reasonablecandidate of electrolyte additives for lithium-ion batteries. However,most of the ionic liquids are readily intercalated into the layerstructure of graphite on the surface of the anode during the batterycharging process, thereby increasing the impedance resistance of the SEIlayer and results in severe generation of lithium precipitation. Theresulting battery exhibits poor cyclic performance. Even with thepresence of film-forming agent and stabilizer, inhibition of theintercalation effect is limited and the generation of the lithiumprecipitation is unavoidable.

SUMMARY OF THE INVENTION

In the first aspect of the invention there is provided an ionic liquidfor adding to an electrolyte of a lithium-ion battery, the ionic liquidcomprises a compound with a dual core structure having the generalformula (I):

-   -   wherein each of cationic group X₁ and X₂ are heterocyclic        aromatic and amine. Preferably, the heterocyclic aromatic is        selected from a group consisting piperidinium, pyrrolidinium,        pyrazolium and pyridinium.    -   More preferably, the amine is selected from a group consisting        quaternary ammonium, azepane and phosphonium.    -   Yet more preferably, X₁ and X₂ is selected from a group        consisting of:

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane

-   1,5 Bis(1-methylpiperidinium 1-yl) pentane

-   1,5 (1-methylpyrrolidium 1-yl) (1-methylpiperidinium 1-yl) pentane

-   1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane

-   1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane

Preferably, the heterocyclic aromatic does not include imidazolium andmorpholinium.

-   -   More preferably, X₁ and X₂ comprises two different functional        group.    -   Yet more preferably, Y is any one of C3˜C10 alkyl group.    -   Advantageously, X₁YX₂ is selected from a group consisting:

-   1,4 Bis(1-methylpyrrolidium 1-yl) butane

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane

-   1,6 Bis(1-methylpyrrolidium 1-yl) hexatane

-   1,8 Bis(1-methylpyrrolidium 1-yl) octane    -   More advantageously, Y is selected from a group consisting of        sulfonyl, carbonic acid, ether, ketone group and ester.    -   Yet more advantageously, X₁YX₂ is selected from a group        consisting:

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] ether

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate

-   1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one

-   Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate    -   Preferably, the anionic group Z₁ and Z₂ os selected from a group        consisting: PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻        (difluorophosphate), BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻        (BOB⁻, bis(oxalato) borate), BF₂(C₂O₄)⁻ (ODFB⁻,        difluoro(oxalato)borate), CF₃BF₃ ⁻        (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,        bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,        bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl        sulfate).    -   In a second aspect of the invention there is provided an ionic        liquid for adding to an electrolyte of a lithium-ion battery,        the ionic liquid comprises a compound with a dual core structure        having the general formula (I):

-   -   wherein each of cationic group X₁ and X₂ are heterocyclic        aromatic and amine.    -   Preferably, the heterocyclic aromatic is selected from a group        consisting piperidinium, pyrrolidinium, pyrazolium and        pyridinium.    -   More preferably, the amine is selected from a group consisting        quaternary ammonium, azepane and phosphonium.    -   Yet more preferably, Y is any one of C3˜C10 alkyl group.    -   It is preferable that Y is selected from a group consisting of        sulfonyl, carbonic acid, ether, ketone group and ester.    -   Advantageously, X₁YW is selected from a group consisting:

-   Benzyl-2-(1-methylpyrrolidinium 1-yl) ethyl ether

-   Benzyl-4-(1-methylpyrrolidinium 1-yl) butyl ether

-   1-(1-Benzoyl)-1-methyl pyrrolidinium

-   1-(2-Phenacyl)-1-methyl pyrrolidinium

-   1-(Furan 2-yl)-1-methyl pyrrolidinium

-   1-(butyl furan 2-yl)-1-methyl pyrrolidinium

-   1-(2-Furoyl)-1-methyl pyrrolidinium

-   1-Benzensulfonyl-1-methyl pyrrolidinium

-   -   1-p-Toluenesulfonyl-1-methyl pyrrolidinium    -   More advantageously, the anionic group Z₁ and Z₂ of the ionic        liquid with structural formula I and formula II can include PF₆        ⁻ (hexafluorophosphate), POF₂ ⁻ (difluorophosphate), BF₄ ⁻        (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻, bis(oxalato) borate),        BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻        (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,        bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,        bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl        sulfate).    -   In a third aspect of the invention there is provided a lithium        ion battery comprising a positive electrode, a negative        electrode, a separator, an electrolyte and one or more ionic        liquid disclosed herein, wherein an overall amount of ionic        liquid added to the electrolyte is 0.1-15 wt. %.    -   Preferably, the lithium ion battery further comprising a        stabilizer, wherein the stabilizer is a cyclophosphazene        compound.    -   More preferably, the stabilizer is selected from a group        consisting:

-   Hexafluoro cyclotriphosphazene

-   Ethoxy (pentafluoro) cyclotriphosphazene    -   Yet more preferably, amount of stabilizer added to the        electrolyte is 0.1-2.9 wt. %.    -   It is preferable that a SEI film forming agent is added to the        electrolyte.    -   Advantageously, the SEI film forming agent is selected from a        group consisting of fluoroethylene carbonate (FEC), vinylene        carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite        (ES), propylene sulfite (PS), and ethylene sulfate (DTD), and        the combination thereof.    -   More advantageously, the amount of the SEI film forming agent        added to the electrolyte is 0.1-5 wt. %.    -   More advantageously, the electrolyte is an non-aqueous        electrolyte.    -   Yet more advantageously, the non-aqueous electrolyte comprises a        lithium salt selected from a group consisting of LiPF₆, LiClO₄,        LiBF₄, LiSO₃CF₃, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂CF₂CF₃)₂,        LiAsF₆, LiAlCl₄, LiNO₃, LiPOF₂, LiB(C₂O₄)₂, LiBF₂(C₂O₄),        LiCF₃BF₃, or a combination thereof.    -   Preferably, concentration of the lithium salt in the electrolyte        is 0.5˜1.5 mol/L.    -   More preferably, the nonauqeous electrolyte comprises an organic        solvent selected from a group consisting of carbonate,        carboxylate, ether, ketone, and combinations thereof    -   More preferably, the carbonate is selected from a group        consisting ethylene carbonate (EC), propylene carbonate (PC),        diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl        carbonate (DMC), dipropyl carbonate, dibutyl carbonate, and a        combination thereof.    -   Preferably, the carboxylate is carboxylic acid ester.    -   More preferably, the carboxylic acid ester comprises methyl        acetate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl        propionate, ethyl propionate and propyl acetate, and a        combination thereof.    -   It is preferable that the positive electrode comprises an active        material being lithium metal complex oxide compound.    -   It is preferable that the metal element of the lithium metal        complex oxide is selected from a group consisting of transition        metal and non-transition metal.    -   Preferably, the transition metal is selected from a group        consisting vanadium, titanium, chromium, copper, iron, nickel        and cobalt.    -   More preferably, the non-transition metal is selected from a        group consisting aluminum and manganese.    -   Yet more preferably, the negative electrode comprises an active        material selected from a group consisting soft carbon, hard        carbon, artificial graphite, natural graphite, meso carbon micro        bead (MCMB), silicon, silicon oxide compounds, silicon carbon        composites, lithium titanate oxide, and the metals that forms        alloy with lithium.    -   It is preferable that the negative electrode comprises an active        material that is carbon-based, silicon-based or tin-based.    -   Advantageously, the separator comprises a membrane.    -   More advantageously, the membrane comprises a material selected        form a group consisting polyethylene (PE), polypropylene (PP),        polyvinylidene fluoride (PVDF), ceramic material, glass fiber        and a combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be more particularly described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a table that shows the synthesis parameters ofbis(1-methylpyrrolidium) alkyl halide;

FIG. 2 is a table that shows the synthesis parameters of two-corecationic chain halide;

FIG. 3A is a table that shows the synthesis parameters of two-corecationic chain ionic liquid;

FIG. 3B is a continuation of the table in FIG. 3A;

FIG. 4 is a table that shows the synthesis parameters of aromatic bondedto 1-methylpyrrolidinium halide;

FIG. 5 is a table that shows the synthesis parameters of aromatic bondedto cation halide;

FIG. 6A is a table that shows the synthesis parameters of aromaticbonded to cation ionic liquid;

FIG. 6B is a continuation of the table in FIG. 6A;

FIG. 7A is a graph showing results of a liner sweep voltammetry LSV ofPYR₁₃PF₆;

FIG. 7B is a graph showing the circled part in FIG. 7A in a differentscale;

FIG. 8A is a graph showing results of a linear sweep voltammetry LSV ofDiPYR₁₅(PF₆)₂;

FIG. 8B is a graph showing the reading of the circled part in FIG. 8A;

FIG. 9A is a graph showing results of a linear sweep voltammetry LSV ofDiPYR₁₈(PF₆)₂;

FIG. 9B is a graph showing the reading of the circled part in FIG. 9A;

FIG. 10A is a graph showing results of a linear sweep voltammetry LSV ofDiPYR_(IEE)(PF₆)₂;

FIG. 10B is a graph showing the reading of the circled part in FIG. 10A;

FIG. 11A is a graph showing results of a linear sweep voltammetry LSV ofPYRPIP₁₅(PF₆)₂;

FIG. 11B is a graph showing the reading of the circled part in FIG. 11A;

FIG. 12A is a graph showing results of a linear sweep voltammetry LSV ofDiPIP₁₅(PF₆)₂;

FIG. 12B is a graph showing the reading of the circled part in FIG. 12A;

FIG. 13A is a graph showing results of a linear sweep voltammetry LSV ofDiPYR₁₅(PF₆)(BF₄);

FIG. 13B is a graph showing the reading of the circled part in FIG. 13A;

FIG. 14A is a graph showing results of a linear sweep voltammetry LSV ofDiPYR₁₅(PF₆)(BF₄);

FIG. 14B is a graph showing the reading of the circled part in FIG. 14A;

FIG. 15A is a table showing the maximum oxidation potential ofelectrolyte with the two-core structure ionic liquid at the LSV test;

FIG. 15B is a continuation of the table in FIG. 15A;

FIG. 15C is a continuation of the table in FIG. 15A and FIG. 15B;

FIG. 16A is a table showing the maximum oxidation potential ofelectrolyte with aromatic bonded to cation ionic liquid at the LSV test;

FIG. 16B is a continuation of the table in FIG. 16A;

FIG. 17 is a graph showing results of a linear sweep voltammetry LSV ofPYR₁₃PF₆;

FIG. 18A is a graph showing results of a linear sweep voltammetry LSV ofDi PYR₁₅(PF₆)₂;

FIG. 18B is a graph showing results of a linear sweep voltammetry LSV ofDi PYR₁₈(PF₆)₂;

FIG. 19A is a graph showing results of a linear sweep voltammetry LSV ofDiPYR_(IEE)(PF₆)₂;

FIG. 19B is a graph showing results of a linear sweep voltammetry LSV ofPIPPYR15(PF₆)₂;

FIG. 19C is a graph showing results of a linear sweep voltammetry LSV ofDiPIP₁₅(PF₆)₂;

FIG. 19D is a graph showing results of a linear sweep voltammetry LSV ofDiPYR₁₅(PF₆)(BF₄);

FIG. 20 is a graph showing results of Li₂CO₃ product, PYRTEA₁₅(PF₆)₂added at 6 wt. % to the OE, DiPYR₁₅(PF₆)₂ added at 6 wt. % to the OE andDiPYR_(IEE)(PF₆)₂ added at 6 wt. % to the OE as well as an organicelectrolyte (OE) being tested by X-ray absorption spectrum O K-edge TEY;

FIG. 21A is a table showing the composition of different electrolyteformulas;

FIG. 21B is a continuation of the table in FIG. 21A;

FIG. 22A shows a top plan view of a LFP battery (Lithium-ion battery) inaccordance with the invention;

FIG. 22B shows a side view of the LFP batter in FIG. 22A;

FIG. 23A is a table showing results of the self-extinguishing time ofvarious electrolyte formulations and its internal impedance andlong-cycle performance of lithium-ion battery; and

FIG. 23B is a continuation of the table in FIG. 23A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The first aspect of the invention relates to an ionic liquid with dualcore cationic chain and aromatic functional group bonded to cation (dualcore structure). It has a high melting point and a wide potentialwindow, is not easy to intercalate into graphite layer of anodematerials, and can form a solid electrolyte interface (SEI) withuniform, compact, and high lithium diffusion reversibility on thesurface of the anode. The ionic liquid is added to the non-aqueouselectrolyte, to enhance the long-term cyclic stability of the highcompacted density electrode and improve the thermal stability of theresulting lithium ion battery.

The dual-core structure increases the structural volume of the cationmuch bigger such that it becomes too large for intercalation ingraphite. A uniform and dense SEI layer is formed on the surface ofgraphite for reversible intercalation and release of lithium ions. Thisreduces the interface impedance and enhance the long-term cyclicstability for the lithium-ion battery. Furthermore, the SEI layer withhigh flame retardancy produced after adding the ionic liquid to theelectrolyte can absorb internal heat and inhibit thermal runaway.

As discussed above, the dual core cation is characterized by an aromaticcompound, amine salt and heterocyclic compound.

The second aspect of the invention involves the use of the ionic liquidin the first aspect of the invention with a non-aqueous electrolyte.

The third aspect of the invention is related to a lithium-ion batterywith the non-aqueous electrolyte in the second aspect and the ionicliquid in the second aspect.

In more detail, the dual-core structure of ionic liquid has the twofunctional groups chain. It is made up of a dual-core cationic chain andan aromatic functional group bonded to cations in the dual-core cationicchain. The dual-core structure has a general formula of Z₁X₁YX₂Z₂ andZ₁X₁YW, with their chemical structural formulas shown below as structureI and structure II, respectively.

The cationic group X₁ and X₂ in structural formula I and the cationicgroup X₁ in structural formula II are selected from a group consistingheterocyclic aromatics and amine salt. The heterocyclic aromaticsincludes piperidinium, pyrrolidinium, pyrazolium and pyridinium, whilethe amine salt includes quaternary ammonium, azepane and phosphonium.

More specifically, the cationic group X₁ and X₂ in structural formula Iand the cationic group X₁ in structural formula II are selected from:

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane,

-   1,5 Bis(1-methylpiperidinium 1-yl) pentane,

-   1,5 (1-methylpyrrolidium 1-yl) (1-methylpiperidinium 1-yl) pentane,

-   1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane,    and/or

-   1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane.

The functional group Y of the ionic liquid with structural formula I andformula II is alkyl group, R indicates the number of carbon atom in thealkyl group, wherein the R=3-10 in particular it is selected from:

-   1,4 Bis(1-methylpyrrolidium 1-yl) butane,

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane,

-   1,6 Bis (1-methylpyrrolidium 1-yl) hexatane, and/or

-   1,8 Bis(1-methylpyrrolidium 1-yl) octane

The functional group Y of the ionic liquid with structural formula I andformula II is selected from sulfonyl, carbonic acid, ether, ketone groupor ester. In particular, the function group Y is selected from:

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] ether,

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate,

-   1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one, and/or

-   Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate

The cationic group X₁, the functional group Y and the aromatic group Wof the ionic liquid with structural formula II is selected from:

-   Benzyl-2-(1-methylpyrrolidinium 1-yl) ethyl ether,

-   Benzyl-4-(1-methylpyrrolidinium 1-yl) butyl ether,

-   1-(1-Benzoyl)-1-methyl pyrrolidinium,

-   1-(2-Phenacyl)-1-methyl pyrrolidinium,

-   1-(Furan 2-yl)-1-methyl pyrrolidinium,

-   1-(butyl furan 2-yl)-1-methyl pyrrolidinium,

-   1-(2-Furoyl)-1-methyl pyrrolidinium,

-   1-Benzensulfonyl-1-methyl pyrrolidinium, and/or

-   1-p-Toluenesulfonyl-1-methyl pyrrolidinium.

The anionic group Z₁ and Z₂ of the ionic liquid with structural formulaI and formula II may include PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻(difluorophosphate), BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻,bis(oxalato) borate), BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate),CF₃BF₃ ⁻ (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI—,bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,bis(trifluoromethane)sulfonamide), and/or CH₃SO₄ ⁻ (MeSO₄ ⁻, methylsulfate).

The weight percentage of the ionic liquid in the electrolyte is 0.1-15wt. %. When the added amount of ionic liquid is too low, the improvementeffect of the electrolyte on the surface of anode is not obvious, butthat is too high, the thickness of SEI layer formed will be much larger,consequently increases the interface impedance between the cathode andanode, resulting in the decline of battery performance.

The non-aqueous electrolyte, including lithium salt, organic solvent,film-forming agent, stabilizer and ionic liquid.

The stabilizer in the non-aqueous electrolyte is a cyclophosphazenecompound, preferably selected from the followings:

Hexafluoro cyclotriphosphazene, and/or

Ethoxy (pentafluoro) cyclotriphosphazene.

The cyclophosphazene compound contains P and F which are both highlyefficient flame retardants. The presence of P and F allow for reductionin the amount of ionic liquid to be added into the electrolyte withnoticeable thermal stability advantage. F assists in generating more LiFon the SEI film formed on the surface of the electrode. The LiF on theSEI film acts as a good oxidation resister to increase the compatibilitybetween the electrolyte and any active materials in the electrode byreducing the reaction between them and the production of unwantedby-product. This in turns stabilizes the electrochemical reaction ofelectrodes and improves the long term cyclic performance of lithium-ionbatteries with high-voltage. The proposed amount of stabilizer in theelectrolyte is 0.1-2.9 wt. %.

The SEI film forming agent in the non-aqueous electrolyte is selectedfrom one or more of fluoroethylene carbonate (FEC), vinylene carbonate(VC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), propylenesulfite (PS), and ethylene sulfate (DTD).

The film-forming agent has a higher reduction potential and can bepreferentially reduced as SEI film on the surface of the graphiteelectrode. The inorganic lithium compound containing sulfur and fluorineis more stable, and it is beneficial to the insertion and release oflithium ions, lower the reduction and decomposition rate of theelectrolyte as well as the occurrence of undesirable side reaction onthe surface of negative electrode. The preferred amount of SEIfilm-forming agent in the electrolyte is 0.1-5 wt. %. It is a finebalance. Too low an amount of the SEI film-forming agent will resultinsignificant improvement on the surface of the electrode, while toolarge an amount of the SEI film-forming agent results in undesirablethickening of the SEI film as this will affect the capacity retention ofthe battery which brings about a decline in the cyclic performance ofthe overall battery.

The lithium salt in the non-aqueous electrolyte includes any one ofLiPF₆, LiClO₄, LiBF₄, LiSO₃CF₃, LiN(SO₂F)₂, LiN(SO₂CF₃)₂,LiN(SO₂CF₂CF₃)₂, LiAsF₆, LiAlCl₄, LiNO₃, LiPOF₂, LiB(C₂O₄)₂,LiBF₂(C₂O₄), LiCF₃BF₃, or a combination thereof. The preferredconcentration of lithium salt in the electrolyte ranges from 0.5 to 1.5mol/L.

The organic solvent of the non-aqueous electrolyte is selected fromcarbonate, carbonate ester (organic carbonate or organocarbonate),carboxylate, carboxylate ester, ethers, ketones or combinations thereof.Among them, carbonates may be any one of ethylene carbonate (EC),propylene carbonate (PC), diethyl carbonate (DEC), methyl ethylcarbonate (EMC), dimethyl carbonate (DMC), and dipropyl carbonate,Dibutyl carbonate, or a combination thereof. The carboxylic acid estersmay be any one of methyl acetate, ethyl acetate, methyl butyrate, ethylbutyrate, methyl propionate, ethyl propionate, propyl acetate, and acombination thereof.

Other organic solvents is suitably selected from one of a cyclic ethersuch as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, a chainether such as 1,2-dimethoxyethane, 1,2-diethoxy ethane,1,2-dibutoxyethane, an amide such as dimethylformamide, and a sulfidesuch as sulfolane, a lactone such as γ-butyrolactone, γ-valerolactone,or the organic solvents may be a combination of two of the above.

In an embodiment of the invention, there is provided a lithium-ionbattery which has a positive electrode (cathode), a negative electrode(anode), a separator interposed between the positive and negativeelectrodes, and an added non-aqueous electrolyte. The positive andnegative electrodes contain active materials that permit intercalationand exfoliation of lithium ions. Active material of cathode may be anyone or a combination of lithium oxide compounds with metal elements suchas vanadium, titanium, chromium, copper, aluminum, iron, nickel, cobalt,manganese, addition of other transition metals or non-transition metalto the aforementioned lithium transition metal oxides compounds, as wellas mixture thereof. The specific crystal structure may be a layeredlithium containing oxide, a spinel type lithium-containing oxides, or anolivine-type of lithium-containing phosphate compounds, etc. The cathodemay contain one of the aforementioned active materials or a combinationof two of more of those active materials. Active material of anode maybe any one of or a combination of soft carbon, hard carbon, artificialgraphite, natural graphite, meso carbon micro bead (MCMB), silicon,silicon oxide compound, silicon carbon composite, lithium titanateoxide, and metals that can form alloys with lithium, etc. Specifically,a carbon-based, silicon-based, tin-based negative electrode can be used.The anode may contain one or more of the aforementioned activematerials.

In the above-mentioned lithium-ion battery, the positive and negativeelectrodes further include a binder and a conductive agent. A slurry ofcathode material which contains the cathode active material, a binderand a conductive agent is coated on a current collector of positiveelectrode. The positive electrode is formed after the slurry dries.Similarly, the slurry of anode material which may include an anodeactive material, a binder and a conductive agent is coated on thecurrent collector of a negative electrode. The negative electrode isobtained after the slurry dries.

The separator may be formed from any material that is commerciallyavailable for making suitable separators in commercial batteries such asbut not limited to polyethylene (PE), polypropylene (PP), polyvinylidenefluoride (PVDF), ceramics materials, glass fibers or composite films ofa combination of the above listed.

The electrolyte is the non-aqueous electrolyte as described.

The following embodiments are provided as examples only for explainingthe invention.

Embodiment 1

The synthesis of ionic liquid with two-core cationic chain (structuralformula I: Z₁X₁YX₂Z₂)

Step 1. Synthesis of Two-Core Cationic Halide

-   -   1. Taking the synthesis of 1,4-bis(1-methylpyrrolidium 1-yl)        butane dichloride (DiPYR₁₄Cl₂) as an example: N-methyl        pyrrolidine (NMPD) is purified by distillation at 85° C., and        then mixed them at the mole ratio of NMPD:1,4-dichlorobutane at        2:1.1, followed by the addition of acetone which is at a volume        same as that of the dichloroalkyl. It is then mixed and stirred        at 70° C. for 16 hours and distilled to remove the acetone. The        resulting liquid is DiPYR₁₄Cl₂.    -   2. Change the alkyl chain Y to other functional groups, such as        sulfonyl, carbonate, ether, ketone, ester, etc. Taking the        synthesis of bis [2-(1-methylpyrrolidinium 1-yl) ethyl] ether        dichloride (DiPYR_(IEE)Cl₂) as an example (No. 8 of FIG. 1/Table        1): Firstly, N-methyl pyrrolidine (NMPD) is purified by        distillation at 85° C., and then NMPD and bis(2-chloroethyl)        ether are mixed at a mole ratio of 2:1.1 followed by the        addition of acetone which is at a volume same as the        bis(2-chloroethyl) ether. It is then mixed and stirred at 70° C.        for 16 hours and distilled to remove the acetone. The resulting        liquid is DiPYR_(IEE)Cl₂.

The synthesis parameters of other series of bis(1-methylpyrrolidium)alkyl halide ionic liquids are shown in FIG. 1/Table 1.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₄Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,4-Dichlorobutane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,4-Dichlorobutane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₄Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₅Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,5-Dichloropentane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,5-Dichloropentane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₅Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₆Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,6-Dichlorohexane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,6-Dichlorohexane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₆Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₇Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,7-Dichloroheptane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,7-Dichloroheptane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₇Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₈Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,8-Dichlorooctane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,8-Dichlorooctane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₈Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₉Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,9-Dichlorononane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,9-Dichlorononane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₉Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR₁₁₀Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,10-Dichlorodecane are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,10-Dichlorodecane.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR₁₁₀Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR_(IEE)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and Bis(2-chloroethyl)ether are mixed at a mole ratio of        2:1.1.    -   3) Addition of acetone which is at a volume same as the        Bis(2-chloroethyl)ether.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR_(IEE)Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR_(IEC)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and Bis(2-chloroethyl) carbonate are mixed at a mole        ratio of 2:1.1.    -   3) Addition of acetone which is at a volume same as the        Bis(2-chloroethyl) carbonate.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR_(IEC)Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR_(IPO)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and 1,5-dichloro pentan-3-one are mixed at a mole ratio        of 2:1.1.    -   3) Addition of acetone which is at a volume same as the        1,5-dichloro pentan-3-one.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR_(IPO)Cl₂.

With reference to FIG. 1/Table 1, the synthesis of DiPYR_(IEB)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,    -   2) NMPD and Bis(2-chloroethyl) butanedioate are mixed at a mole        ratio of 2:1.1.    -   3) Addition of acetone which is at a volume same as the        Bis(2-chloroethyl) butanedioate.    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Distilled to remove the acetone. The resulting liquid is        DiPYR_(IEB)Cl₂.        -   3. Replacing the cations X₁ and X₂ with other heterocyclic            aromatic or amine, which may include imidazolium, quaternary            ammonium, piperidinium, pyrrolidinium, morpholinium,            trimethylamine, etc. Taking the synthesis of            1,5-bis(1-methylpiperidinium 1-yl) pentane dichloride            (DiPIP₁₅Cl₂) as an example: N-methyl piperidine (MPIP) is            purified by vacuum distillation, and then MPIP and            1,5-dichloropentane are mixed at the mole ratio of 2:1.1            followed by the addition of acetone which has a volume same            as that of the dichloroalkyl. It is then mixed and stirred            at 70° C. for 16 hours. After distilling off the acetone,            the remaining liquid is DiPIP₁₅Cl₂.    -   Taking the synthesis of 1,5-(1-methylpyrrolidium        1-yl)(1-methylpiperidinium 1-yl) pentane dichloride        (PYRPIP₁₅Cl₂) as an example (no. 5 of FIG. 2/Table 2). N-methyl        pyrrolidine (NMPD) and N-methyl piperidine (MPIP) are purified        by vacuum distillation. NMPD, MPIP, and 1,5-Dichloropentane are        mixed at a mole ratio of 1:1:1.1 followed by the addition of        acetone which is in the same volume as the 1,5-Dichloropentane.        It is then mixed and stirred at 70° C. for 16 hours. After the        acetone is distilled off, the remaining liquid is PYRPIP₁₅Cl₂.        The synthesis parameters of other series of two-core cationic        halide ionic liquid are shown in FIG. 2/Table 2

With reference to FIG. 2/Table 2, the synthesis of DiPYR₁₅Cl₂:

-   -   1) N-methyl pyrrolidine (NMPD) is purified by distillation at        85° C.    -   2) NMPD and 1,5-Dichloropentane are mixed at a mole ratio of        2:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Acetone is distilled off and the remaining liquid is        DiPYR₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of DiPIP₁₅Cl₂:

-   -   1) N-methyl piperidine (MPIP) is purified by vacuum        distillation.    -   2) MPIP and 1,5-Dichloropentane are mixed at a mole ratio of        2:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Acetone is distilled off and the remaining liquid is        DiPIP₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of DiTEA₁₅Cl₂:

-   -   1) Triethylamine (TEA) is purified by vacuum distillation.    -   2) TEA and 1,5-Dichloropentane are mixed at a mole ratio of        2:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Acetone is distilled off and the remaining liquid is        DiTEA₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of DiMIM₁₅Cl₂:

-   -   1) 1-methylimidazole (MIM) is purified by vacuum distillation.    -   2) MIM and 1,5-Dichloropentane are mixed at a mole ratio of        2:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        DiMIM₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PYRPIP₁₅Cl₂:

-   -   1) NMPD and MPIP are purified by vacuum distillation.    -   2) NMPD and MPIP and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Acetone is distilled off and the remaining liquid is        PYRPIP₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PYRTEA₁₅Cl₂:

-   -   1) NMPD and TEA are purified by vacuum distillation.    -   2) NMPD and TEA and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Acetone is distilled off and the remaining liquid is        PYRTEA₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PYRMPE₁₅Cl₂:

-   -   1) NMPD and Morpholine (MPE) are purified by vacuum        distillation.    -   2) NMPD and MPE and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        PYRMPE₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PYRMIM₁₅Cl₂:

-   -   1) NMPD and MIM are purified by vacuum distillation.    -   2) NMPD and MIM and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        PYRMPE₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PYRPYO₁₅Cl₂:

-   -   1) NMPD and Pyrrole (PYO) are purified by vacuum distillation.    -   2) NMPD and PYO and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        PYRPYO₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PIPTEA₁₅Cl₂:

-   -   1) MPIP and TEA are purified by vacuum distillation.    -   2) MPIP and TEA and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 70° C. for 16 hours.    -   5) Acetone is distilled off and the remaining liquid is        PIPTEA₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PIPMPE₁₅Cl₂:

-   -   1) MPIP and MPE are purified by vacuum distillation.    -   2) MPIP and MPE and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        PIPMPE₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PIPMIM₁₅Cl₂:

-   -   1) MPIP and MIM are purified by vacuum distillation.    -   2) MPIP and MIM and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        PIPMIM₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of PIPPYO₁₅Cl₂:

-   -   1) MPIP and PYO are purified by vacuum distillation.    -   2) MPIP and PYO and 1,5-Dichloropentane are mixed at a mole        ratio of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        PIPPYO₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of TEAMPE₁₅Cl₂:

-   -   1) TEA and MPE are purified by vacuum distillation.    -   2) TEA and MPE and 1,5-Dichloropentane are mixed at a mole ratio        of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        TEAMPE₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of TEAMIM₁₅Cl₂:

-   -   1) TEA and MIM are purified by vacuum distillation.    -   2) TEA and MIM and 1,5-Dichloropentane are mixed at a mole ratio        of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        TEAMIM₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of TEAPYO₁₅Cl₂:

-   -   1) TEA and PYO are purified by vacuum distillation.    -   2) TEA and PYO and 1,5-Dichloropentane are mixed at a mole ratio        of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        TEAPYO₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of MIMMPE₁₅Cl₂:

-   -   1) MIM and MPE are purified by vacuum distillation.    -   2) MIM and MPE and 1,5-Dichloropentane are mixed at a mole ratio        of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        MIMMPE₁₅Cl₂.

With reference to FIG. 2/Table 2, the synthesis of MIMPYO₁₅Cl₂:

-   -   1) MIM and PYO are purified by vacuum distillation.    -   2) MIM and PYO and 1,5-Dichloropentane are mixed at a mole ratio        of 1:1:1.1    -   3) Adding acetone which is in the same volume as the        1,5-Dichloropentane    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off and the remaining liquid is        MIMPYO₁₅Cl₂.

Step 2. Synthesis of Two-Core Cationic Chain Ionic Liquid

-   1. Taking the synthesis of 1,4-bis(1-methylpyrrolidium 1-yl) butane    dihexafluorophosphate [DiPYR₁₄(PF₆)₂] as an example:    1,4-bis(1-methylpyrrolidium 1-yl) butane dichloride (DiPYR₁₄Cl₂)    synthesized in Step 1 is added to an equal weight of acetone (as a    mixed solvent). followed by adding twice as many mole of potassium    hexafluorophosphate. It is stirred at 70° C. for 16 hours. After    filtering the white precipitate potassium chloride KCl, the    remaining liquid is distilled under reduced pressure to remove the    acetone, and then recrystallized to form DiPYR₁₄(PF₆)₂. Finally, the    synthesized product is filtered, purified and dried in a vacuum oven    at 60° C. until its water content is less than 20 ppm. The synthesis    parameters of other series of DiPYR_(1R)(PF₆)₂ and DiPIP_(1R)(PF₆)₂    ionic liquids are shown in FIG. 3A or Table 3.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPYR₁₄(PF₆)₂:    -   1) DiPYR₁₄Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₄(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPYR₁₅(PF₆)₂:    -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₅(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPYR₁₆(PF₆)₂:    -   1) DiPYR₁₆Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₆(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPYR₁₈(PF₆)₂:    -   1) DiPYR₁₈Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₈(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPIP₁₄(PF₆)₂:    -   1) DiPIP₁₄(PF₆)₂ synthesized in Step 2 is added to an equal        weight of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₄(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPIP₁₅(PF₆)₂:    -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₅(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPIP₁₆(PF₆)₂:    -   1) DiPIP₁₆Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₆(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        DiPIP₁₈(PF₆)₂:    -   1) DiPIP₁₈Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₈(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.-   2. Replacing the cation X₁ and X₂ with other heterocyclic aromatics    or amine, including imidazolium, quaternary ammonium, piperidinium,    pyrrolidinium, morpholinium, and triethylamine etc. Taking the    synthesis of 1,5-(1-methylpyrrolidium 1-yl)(1-methyl piperidinium    1-yl) pentane dihexafluorophosphate [PYRPIP₁₅(PF₆)₂] as an example:    The 1,5-(1-methylpyrrolidium 1-yl)(1-methylpiperidinium 1-yl)    pentane dichloride (PYRPIP₁₅Cl₂) synthesized in Step 1 is added to    an equal weight of acetone (as a mixed solvent). Twice the mole of    potassium hexafluorophosphate is then added. It is stirred at 70° C.    for 16 hours. After the white precipitate potassium chloride KCl is    filtered, the remaining liquid is distilled under reduced pressure    to remove the acetone, and then recrystallized to form    PYRPIP₁₅(PF₆)₂. Finally, the synthesized product is filtered and    purified and dried in a vacuum oven at 60° C. until its water    content is less than 20 ppm. The synthesis parameters of other    series of two-core cationic chain ionic liquids are shown in FIGS.    3A, 3B or Table 3.    -   With reference to FIG. 3A/Table 3, the synthesis of        PYRPIP₁₅(PF₆)₂:    -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRPIP₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PYRTEA₁₅(PF₆)₂:    -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRTEA₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PYRMPE₁₅(PF₆)₂:    -   1) PYRMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRMPE₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PYRMIM₁₅(PF₆)₂:    -   1) PYRMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRMIM₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PYRPYO₁₅(PF₆)₂:    -   1) PYRPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRPYO₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PIPTEA₁₅(PF₆)₂:    -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPTEA₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PIPMPE₁₅(PF₆)₂:    -   1) PIPMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPMPE₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PIPMIM₁₅(PF₆)₂:    -   1) PIPMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPMIM₁₅(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        PIPPYO₁₅(PF₆)₂:    -   1) PIPPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPPYO₁₅(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        TEAMPE₁₅(PF₆)₂:    -   1) TEAMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form TEAMPE₁₅(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of        TEAMIM₁₅(PF₆)₂:    -   1) TEAMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form TEAMIM₁₅(PF₆)₂.    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        TEAPYO₁₅(PF₆)₂:    -   1) TEAPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form TEAPYO₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        MIMMPE₁₅(PF₆)₂:    -   1) MIMMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form MIMMPE₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        MIMPYO₁₅(PF₆)₂:    -   1) MIMPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding twice as many moles of potassium hexafluorophosphate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form MIMPYO₁₅(PF₆)₂    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.-   3. Replacing the other anion Z₁ and Z₂, which may include PF₆ ⁻    (hexafluorophosphate), POF₂ ⁻ (difluorophosphate), BF₄ ⁻    (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻, bis(oxalato) borate),    BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻    (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,    bis(fluorosulfonyl)imide), (CF₃SO₂)₂N (TFSI⁻,    bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl    sulfate), etc.    -   Taking the synthesis of 1,5-(1-methylpyrrolidium        1-yl)(1-methylpiperidinium) 1-yl) pentane hexafluorophosphate        tetrafluoroborate [PYRPIP₁₅(PF₆)(BF₄)] as an example. The        1,5-(1-methylpyrrolidium 1-yl)(1-methylpiperidinium 1-yl)        pentane dichloride (PYRPIP₁₅Cl₂) synthesized in Step 1 is added        to an equal weight of acetone (as a mixed solvent) followed by        the addition of same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate. It is stirred at 70° C. for 16        hours. After the white precipitate potassium chloride KCl is        filtered, the remaining liquid is distilled under reduced        pressure to remove the acetone, and then recrystallized to form        PYRPIP₁₅(PF₆)(BF₄). Finally, the synthesized product is        filtered, purified, and dried in a vacuum oven at 60° C. to        until its water content is below 20 ppm. The synthesis        parameters of other series of two-core cationic chain ionic        liquids are shown in FIGS. 3A/3B/Table 3.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₄(PF₆)        (BF₄):    -   1) DiPYR₁₄Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₄(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₅(PF₆)        (BF₄):    -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight        of acetone    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₅(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₆(PF₆)        (BF₄):    -   1) DiPYR₁₆Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₆(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₈(PF₆)        (BF₄):    -   1) DiPYR₁₈Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₈(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₄(PF₆)        (BF₄):    -   1) DiPIP₁₄Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₄(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₅(PF₆) (BF₄):

-   -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₅(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₆(PF₆)        (BF₄):    -   1) DiPIP₁₆Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₆(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₈(PF₆)        (BF₄):    -   1) DiPIP₁₈Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₈(PF₆) (BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRPIP₁₅(PF₆)(BF₄):    -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRPIP₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRTEA₁₅(PF₆)(BF₄):    -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRTEA₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRMPE₁₅(PF₆)(BF₄):    -   1) PYRMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRMPE₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRMIM₁₅(PF₆)(BF₄):    -   1) PYRMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRMIM₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRPYO₁₅(PF₆)(BF₄):    -   1) PYRPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRPYO₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PIPTEA₁₅(PF₆)(BF₄):    -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPTEA₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PIPMPE₁₅(PF₆)(BF₄):    -   1) PIPMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPMPE₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PIPMIM₁₅(PF₆)(BF₄):    -   1) PIPMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPMIM₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PIPPYO₁₅(PF₆)(BF₄):    -   1) PIPPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPPYO₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        TEAMPE₁₅(PF₆)(BF₄):    -   1) TEAMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form TEAMPE₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        TEAMIM₁₅(PF₆)(BF₄):    -   1) TEAMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 25° C. for 12 hours    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form TEAMIM₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        TEAPYO₁₅(PF₆)(BF₄):    -   1) TEAPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 45° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form TEAPYO₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        MIMMPE₁₅(PF₆)(BF₄):    -   1) MIMMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form MIMMPE₁₅(PF₆)(BF₄):    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        MIMPYO₁₅(PF₆)(BF₄):    -   1) MIMPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of potassium hexafluorophosphate and        potassium tetrafluoroborate.    -   3) Stir at 25° C. for 12 hours.    -   4) Filtering the white precipitate KCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form MIMPYO₁₅(PF₆)(BF₄).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        DiPYR₁₅(TFSI)(FSI):    -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium trifluoromethanesulfonimide and        lithium bis(fluorosulfonyl)imide.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₅(TFSI)(FSI).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        DiPIP₁₅(TFSI)(FSI):    -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide        and lithium bis(fluorosulfonyl)imide.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₅(TFSI)(FSI).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRPIP₁₅(TFSI)(FSI):    -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide        and lithium bis(fluorosulfonyl)imide.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRPIP₁₅(TFSI)(FSI).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRTEA₁₅(TFSI)(FSI):    -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide        and lithium bis(fluorosulfonyl)imide.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRTEA₁₅(TFSI)(FSI).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PIPTEA₁₅(TFSI)(FSI):    -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide        and lithium bis(fluorosulfonyl)imide    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPTEA₁₅(TFSI)(FSI).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        DiPYR₁₅(CF₃BF₃)(POF₂):    -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate        and lithium difluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPYR₁₅(CF₃BF₃)(POF₂).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        DiPIP₁₅(CF₃BF₃)(POF₂):    -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate        and lithium difluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form DiPIP₁₅(CF₃BF₃)(POF₂).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRPIP₁₅(CF₃BF₃)(POF₂):    -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate        and lithium difluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRPIP₁₅(CF₃BF₃)(POF₂).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PYRTEA₁₅(CF₃BF₃)(POF₂):    -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate        and lithium difluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PYRTEA₁₅(CF₃BF₃)(POF₂).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.    -   With reference to FIG. 3B/Table 3, the synthesis of        PIPTEA₁₅(CF₃BF₃)(POF₂):    -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight        of acetone.    -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate        and lithium difluorophosphate.    -   3) Stir at 70° C. for 16 hours.    -   4) Filtering the white precipitate LiCl.    -   5) Distill the remaining liquid under reduced pressure to remove        the acetone.    -   6) Recrystallize to form PIPTEA₁₅(CF₃BF₃)(POF₂).    -   7) The product is filtered, purified and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

Embodiment 2

Synthesis of Ionic Liquid with the Aromatic Functional Group Bonded to aCation (Structural Formula II: Z₁X₁YW)

Step 1. Synthesis of Aromatic Group Bonded to Cation Halide

-   1. Taking the synthesis of benzyl-2-(1-methylpyrrolidinium 1-yl)    ethyl ether chloride (Benzyl-PYR_(IEE)Cl) as an example. Firstly,    N-methyl pyrrolidine (NMPD) is purified by distillation at 85° C.    Then NMPD and Benzyl 2-chloroethyl ether are mixed at the mole ratio    of 1:1.1 followed by adding acetone of the same volume as the    benzyl-2-chloroethyl ether. It is mixed and stirred at 70° C. for 12    hours. Acetone is distilled off with the remaining liquid being    benzyl-PYR_(IEE)Cl. The synthesis parameters of other series of    aromatic bonded to 1-methylpyrrolidinium halide are shown in FIG.    4/Table 4.-   2. The synthesis of 1-(2-Furoyl)-1-methyl pyrrolidinium chloride    (Furoyl-PYR₁₁Cl) as an example. First, N-methyl pyrrolidine (NMPD)    is purified by distillation at 85° C. Then NMPD and 2-Furoyl    chloride are mixed at a mole ratio of 1:1.1 followed by adding    acetone at the same volume as the 2-furoyl chloride. It is then    mixed and stirred at 70° C. for 12 hours. Acetone is removed by    distillation and the remaining liquid is Furoyl-PYR₁₁Cl. The    synthesis parameters of other series of aromatic bonded to    1-methylpyrrolidinium halide are shown in FIG. 4/Table 4.    -   With reference to FIG. 4/Table 4, the synthesis of        Benzyl-PYR_(IEE)Cl:    -   1) NMPD is purified by distillation at 85° C.    -   2) NMPD and Benzyl-2-chloroethyl ether are mixed at the mole        ratio of 1:1.1.    -   3) Adding acetone of the same volume as the Benzyl-2-chloroethyl        ether.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid being        Benzyl-PYR_(IEE)Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Benzyl-PYR_(IBE)Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and Benzyl-4-chloro butyl ether are mixed at the            mole ratio of 1:1.1.        -   3) Adding acetone of the same volume as the Benzyl-4-chloro            butyl ether.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Benzyl-PYR_(IBE)Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Benzoyl-PYR₁₁Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and Benzoyl chloride are mixed at the mole ratio of            1:1.1.        -   3) Adding acetone of the same volume as the Benzoyl            chloride.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Benzoyl-PYR₁₁Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Phenacyl-PYR₁₁Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and Phenacyl chloride are mixed at the mole ratio of            1:1.1.        -   3) Adding acetone of the same volume as the Phenacyl            chloride.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Phenacyl-PYR₁₁Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Furan-PYR₁₁Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and 2-Chlorofuran are mixed at the mole ratio of            1:1.1.        -   3) Adding acetone of the same volume as the 2-Chlorofuran.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Furan-PYR₁₁Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Furan-PYR₁₄Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and 2-(4-chlorobutyl)furan are mixed at the mole            ratio of 1:1.1.        -   3) Adding acetone of the same volume as the            2-(4-chlorobutyl)furan.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Furan-PYR₁₄Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Furoyl-PYR₁₁Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and 2-Furoyl chloride are mixed at the mole ratio of            1:1.1.        -   3) Adding acetone of the same volume as the 2-Furoyl            chloride.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Furoyl-PYR₁₁Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        Benzenesulfonyl-PYR₁₁Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and Benzenesulfonyl chloride are mixed at the mole            ratio of 1:1.1.        -   3) Adding acetone of the same volume as the Benzenesulfonyl            chloride.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            Benzenesulfonyl-PYR₁₁Cl.    -   With reference to FIG. 4/Table 4, the synthesis of        p-Toluenesulfonyl-PYR₁₁Cl:        -   1) NMPD is purified by distillation at 85° C.        -   2) NMPD and p-Toluenesulfonyl chloride are mixed at the mole            ratio of 1:1.1.        -   3) Adding acetone of the same volume as the            p-Toluenesulfonyl chloride.        -   4) Mix and stir at 70° C. for 12 hours.        -   5) Acetone is distilled off with the remaining liquid being            p-Toluenesulfonyl-PYR₁₁Cl.-   3. Replacing the cation X₁ with other heterocyclic aromatic or amine    such as imidazolium, quaternary ammonium, piperidinium,    pyrrolidinium, morpholinium, triethylamine etc. Taking the synthesis    of 1-(2-Furoyl)-1-methyl piperidinium chloride (Furoyl-PIP₁₁Cl) as    an example. Firstly, N-methyl piperidine (MPIP) is purified by    vacuum distillation, and then the MPIP and 2-Furoyl chloride are    mixed at a mole ratio of 1:1.1. Acetone, same volume as 2-furoyl    chloride, is added. It is mixed and stirred at 70° C. for 12 hours.    Acetone is distilled off with the remaining liquid as    Furoyl-PIP₁₁Cl. The synthesis parameters of other series of aromatic    bonded to cation halide ionic liquids are shown in FIG. 5/Table 5.

With reference to FIG. 5/Table 5, the synthesis of Benzyl-PYR_(IEE)Cl:

-   -   1) NMPD is purified by distillation at 85° C.    -   2) NMPD and Benzyl 2-chloroethyl ether are mixed at a mole ratio        of 1:1.1.    -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Benzyl-PYR_(IEE)Cl.

With reference to FIG. 5/Table 5, the synthesis of Furan-PYR₁₄Cl:

-   -   1) NMPD is purified by distillation at 85° C.    -   2) NMPD and 2-(4-chlorobutyl)furan are mixed at a mole ratio of        1:1.1.    -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furan-PYR₁₄Cl.

With reference to FIG. 5/Table 5, the synthesis of Furoyl-PYR₁₁Cl:

-   -   1) NMPD is purified by distillation at 85° C.    -   2) NMPD and 2-Furoyl chloride are mixed at a mole ratio of        1:1.1.    -   3) Acetone, same volume as 2-Furoyl chloride, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furoyl-PYR₁₁Cl.

With reference to FIG. 5/Table 5, the synthesis of Benzyl-PIP_(IEE)Cl:

-   -   1) MPIP is purified by vacuum distillation.    -   2) MPIP and Benzyl 2-chloroethyl ether are mixed at a mole ratio        of 1:1.1.    -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Benzyl-PIP_(IEE)Cl.

With reference to FIG. 5/Table 5, the synthesis of Furan-PIP₁₄Cl:

-   -   1) MPIP is purified by vacuum distillation.    -   2) MPIP and 2-(4-chlorobutyl)furan are mixed at a mole ratio of        1:1.1.    -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furan-PIP₁₄Cl.

With reference to FIG. 5/Table 5, the synthesis of Furoyl-PIP₁₁Cl:

-   -   1) MPIP is purified by vacuum distillation.    -   2) MPIP and 2-Furoyl chloride are mixed at a mole ratio of        1:1.1.    -   3) Acetone, same volume as 2-Furoyl chloride, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furoyl-PIP₁₁Cl.

With reference to FIG. 5/Table 5, the synthesis of Benzyl-TEA_(IEE)Cl:

-   -   1) TEA is purified by vacuum distillation.    -   2) TEA and Benzyl 2-chloroethyl ether are mixed at a mole ratio        of 1:1.1.    -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Benzyl-TEA_(IEE)Cl.

With reference to FIG. 5/Table 5, the synthesis of Furan-TEA₁₄Cl:

-   -   1) TEA is purified by vacuum distillation.    -   2) TEA and 2-(4-chlorobutyl)furan are mixed at a mole ratio of        1:1.1.    -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furan-TEA₁₄Cl.

With reference to FIG. 5/Table 5, the synthesis of Furoyl-TEA₁₁Cl:

-   -   1) TEA is purified by vacuum distillation.    -   2) TEA and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.    -   3) Acetone, same volume as 2-Furoyl chloride, is added.    -   4) Mix and stir at 70° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furoyl-PIP₁₁Cl.

With reference to FIG. 5/Table 5, the synthesis of Benzyl-MIM_(IEE)Cl:

-   -   1) MIM is purified by vacuum distillation.    -   2) MIM and Benzyl 2-chloroethyl ether are mixed at a mole ratio        of 1:1.1.    -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Benzyl-PYR_(IEE)Cl.

With reference to FIG. 5/Table 5, the synthesis of Furan-MIM₁₄Cl:

-   -   1) MIM is purified by vacuum distillation.    -   2) MIM and 2-(4-chlorobutyl)furan mixed at a mole ratio of        1:1.1.    -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furan-MIM₁₄Cl.

With reference to FIG. 5/Table 5, the synthesis of Furoyl-MIM₁₁Cl:

-   -   1) MIM is purified by vacuum distillation.    -   2) MIM and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.    -   3) Acetone, same volume as 2-Furoyl chloride, is added.    -   4) Mix and stir at 25° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furoyl-MIM₁₁Cl.

With reference to FIG. 5/Table 5, the synthesis of Furoyl-MPE₁₁Cl:

-   -   1) MPE is purified by vacuum distillation.    -   2) MPE and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.    -   3) Acetone, same volume as 2-Furoyl chloride, is added.    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furoyl-MPE₁₁Cl.

With reference to FIG. 5/Table 5, the synthesis of Furoyl-PYO₁₁Cl:

-   -   1) PYO is purified by vacuum distillation.    -   2) PYO and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.    -   3) Acetone, same volume as 2-Furoyl chloride, is added.    -   4) Mix and stir at 45° C. for 12 hours.    -   5) Acetone is distilled off with the remaining liquid as        Furoyl-PYO₁₁Cl.

Step 2. Synthesis of Ionic Liquid with Aromatic Group Bonded to Cation

-   1. Taking the synthesis of 1-(2-Furoyl)-1-methyl pyrrolidinium    hexafluorophosphate (Furoyl-PYR₁₁PF₆) as an example.    1-(2-furoyl)-1-methyl pyrrolidinium chloride (Furoyl-PYR₁₁Cl)    synthesized in Step 1 is added to an equal weight of acetone (as a    mixed solvent) followed by adding a same mole number of potassium    hexafluorophosphate. It is stirred at 70° C. for 12 hours. After the    white precipitate potassium chloride KCl is filtered, the remaining    liquid is distilled under reduced pressure to remove the acetone,    and then recrystallized to form Furoyl-PYR₁₁PF₆. Finally, the    synthesized product is filtered, purified, and dried in a vacuum    oven at 60° C. until its water content is less than 20 ppm. The    synthesis parameters of other series of aromatic bonded to cation    ionic liquid are shown in FIG. 6A, FIG. 6B or Table 6.-   2. Replacing the cation X₁ with other heterocyclic aromatic or    amine, such as imidazolium, quaternary ammonium, piperidinium,    pyrrolidinium, morpholinium, triethylamine etc. Taking the synthesis    of 1-(2-Furoyl)-1-methyl piperidinium hexafluorophosphate    (Furoyl-PIP₁₁PF₆) as an example. 1-(2-furoyl)-1-methyl piperidinium    chloride (Furoyl-PIP₁₁Cl) synthesized in Step 1 is added to an equal    weight of acetone (as a mixed solvent) followed by the same mole    number of potassium hexafluorophosphate. It is stirred at 70° C. for    12 hours. The white precipitate potassium chloride KCl is filtered    out. The remaining liquid is distilled under reduced pressure to    remove acetone, and then recrystallized to form Furoyl-PIP₁₁PF₆.    Finally, the synthesized product is filtered, purified and dried in    a vacuum oven at 60° C. until a water content of less than 20 ppm.    The synthesis parameters of other series of aromatic bonded to    cation ionic liquid are shown in FIG. 6A, FIG. 6B or Table 6.-   3. Replacing anion Z₁ such as PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻    (difluorophosphate), BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻,    bis(oxalato) borate), BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate),    CF₃BF₃ ⁻(trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,    bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,    bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl    sulfate), etc. Taking the synthesis of 1-(2-Furoyl)-1-methyl    pyrrolidinium tetrafluoroborate (Furoyl-PYR₁₁BF₄) as an example.    1-(2-furoyl)-1-methyl pyrrolidinium chloride (Furoyl-PYR₁₁Cl)    synthesized in Step 1 is added to the same weight of acetone (as a    mixed solvent). The same mole number of potassium tetrafluoroborate    is added. It is stirred at 70° C. for 12 hours. The white    precipitate potassium chloride KCl is filtered. The remaining liquid    is distilled under reduced pressure to remove acetone, and then    recrystallized to form Furoyl-PYR₁₁BF₄. Finally, the synthesized    product is filtered purified and dried in a vacuum oven at 60° C.    until its water content is below 20 ppm. The synthesis parameters of    other series of aromatic bonded to cation ionic liquid are shown in    FIG. 6/Table 6.

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-PYR_(IEE)PF₆:

-   -   1) Benzyl-PYR_(IEE)Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzyl-PYR_(IEE)PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A or Table 6, the synthesis ofBenzyl-PYR_(IBE)PF₆:

-   -   1) Benzyl-PYR_(IBE)Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzyl-PYR_(IBE)PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A or Table 6, the synthesis of Benzoyl-PYR₁₁PF₆:

-   -   1) Benzoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzoyl-PYR₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A or table 6, the synthesis ofPhenacyl-PYR₁₁PF₆:

-   -   1) Phenacyl-PYR₁₁ in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Phenacyl-PYR₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-PYR₁₁PF₆:

-   -   1) Furan-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furan-PYR₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-PYR₁₄PF₆:

-   -   1) Furan-PYR₁₄Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furan-PYR₁₄PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-PYR₁₁PF₆:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁PF₆    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis ofBenzenesulfonyl-PYR₁₁PF₆:

-   -   1) Benzenesulfonyl-PYR₁₁Cl in Step 1 is added to an equal weight        of acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzenesulfonyl-PYR₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis ofp-Toluenesulfonyl-PYR₁₁PF₆:

-   -   1) p-Toluenesulfonyl-PYR₁₁Cl in Step 1 is added to an equal        weight of acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form p-Toluenesulfonyl-PYR₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-PIP_(IEE)PF₆:

-   -   1) Benzyl-PIP_(IEE)Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzyl-PIP_(IEE)PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-PIP₁₄PF₆:

-   -   1) Furan-PIP₁₄Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furan-PIP₁₄PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-PIP₁₁PF₆:

-   -   1) Furoyl-PIP₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone    -   6) Recrystallized to form Furoyl-PIP 11PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-TEA_(IEE)PF₆:

-   -   1) Benzyl-TEA_(IEE)Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzyl-TEA_(IEE)PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-TEA₁₄PF₆:

-   -   1) Furan-TEA₁₄Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furan-TEA₁₄PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-TEA₁₁PF₆:

-   -   1) Furoyl-TEA₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone    -   6) Recrystallized to form Furoyl-TEA₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-MIM_(IEE)PF₆:

-   -   1) Benzyl-MIM_(IEE)Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 25° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Benzyl-MIM_(IEE)PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-MIM₁₄PF₆:

-   -   1) Furan-MIM₁₄Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 25° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furan-MIM₁₄PF₆    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-MIM₁₁PF₆:

-   -   1) Furoyl-MIM₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 25° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-MIM₁₁PF₆    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-MPE₁₁PF₆:

-   -   1) Furoyl-MPE₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 45° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-MPE₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYO₁₁PF₆.

-   -   1) Furoyl-PYO₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium hexafluorophosphate is added.    -   3) Stir at 45° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYO₁₁PF₆.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁BF₄:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium tetrafluoroborate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁BF₄.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁FSI.

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of lithiumbis(fluorosulfonyl)imide is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate lithium chloride LiCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁FSI.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁TFSI.

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of lithium bis(trifluoromethane)sulfonamide        is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate lithium chloride LiCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁TFSI.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁CF₃BF₃.

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of lithium trifluoromethyltrifluoroborate is        added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate lithium chloride LiCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁CF₃BF₃.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁POF₂:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of lithium difluorophosphate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate lithium chloride LiCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁POF₂.    -   7) The product is filtered, purified, and dried in a vacuum oven        at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁MeSO₄:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of        acetone.    -   2) Same mole number of potassium methyl sulfate is added.    -   3) Stir at 70° C. for 12 hours.    -   4) White precipitate potassium chloride KCl is filtered.    -   5) Remaining liquid is distilled under reduced pressure to        remove the acetone.    -   6) Recrystallized to form Furoyl-PYR₁₁MeSO₄:

The product is filtered, purified, and dried in a vacuum oven at 60° C.until its water content is less than 20 ppm

Embodiment 3

According to the maximum solubility, an ionic liquid with the two-corecationic chain or an ionic liquid with aromatic bonded to cation isadded to a non-aqueous electrolyte. The amount of ionic liquid is about10-15 wt. % of the electrolyte. Then, a linear sweep voltammetry (LSV)is conducted using the AutoLab 302N electrochemistry to obtain themaximum oxidation potential of the electrolyte.

Testing Conditions of LSV:

working electrode Pt, reference electrode Li, counter electrode Li, scanvoltage range 0.5˜5.0 V, scan rate 0.03 V/s.

-   1. Traditional ionic liquid with aromatic heterocycle:    1-propyl-1-methylpyrrolidium hexafluorophosphate (PYR₁₃PF₆)    -   Electrolyte: 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt.        % PYR₁₃PF₆    -   With reference to FIGS. 7A and 7B, the LSV test shows that the        lithium deposition/dissolution reaction at low potential. A        corrosion current greater than 5×10⁻⁵ (Amp.) occurred at the        high potential of 4.742V in the first cycle. That is an        oxidation reaction, which means that the maximum oxidation        potential of the organic electrolyte with adding 15 wt. %        PYR₁₃PF₆ is 4.742 V. The potential window of that is about        0-4.742 V. There is no side reaction in this electrolyte within        this working voltage range.-   2. Two-core cationic chain ionic liquid: 1,5 bis(1-methylpyrrolidium    1-yl) pentane dihexafluorophosphate [DiPYR₁₅(PF₆)₂], 1,8    bis(1-methylpyrrolidium 1-yl) octane dihexafluorophosphate    [DiPYR₁₈(PF₆)₂]    -   Electrolyte:        -   (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %            DiPYR₁₅(PF₆)₂,        -   (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %            DiPYR₁₈(PF₆)₂        -   With reference to FIGS. 8A and 8B, the LSV test showed that            the lithium deposition/dissolution reaction also occurs at            low potential. The corrosion current greater than 5×10⁻⁵            (Amp.) occurred at the high potential of 4.922V in the first            cycle. This means that the maximum oxidation potential of            the organic electrolyte with 10 wt. % DiPYR₁₅(PF₆)₂ added is            4.922V. The potential window is about 0-4.922 V which            indicates that the addition of DiPYR₁₅(PF₆)₂ can increase            the maximum oxidation potential of the electrolyte, reduces            the dissociation reaction under the high working voltage,            and inhibits the growth of internal impedance in the            lithium-ion battery.        -   With reference to FIGS. 9A and 9B, the LSV test shows that            there was no corrosion current greater than 5×10⁻⁵ (Amp.) at            a high voltage of 5.02 V in the first cycle. This means that            the maximum oxidation potential of organic electrolyte with            adding 10 wt. % DiPYR₁₈(PF₆)₂ is greater than 5.0V. It            indicates that the addition of DiPYR₁₈(PF₆)₂ can increase            the maximum oxidation potential of the electrolyte with the            ability of withstanding high voltage being better than that            of the addition of DiPYR₁₅(PF₆)₂.-   4. Replacing the alkyl chain Y with other functional groups,    replacing the cation X₁ and X₂ with other heterocyclic aromatic or    amine, or replacing the anion Z₁ and Z₂. Taking the following ionic    liquids with two-core cationic chain as examples: bis    [2-(1-methylpyrrolidinium 1-yl) ethyl] ether dihexafluorophosphate    [DiPYR_(IEE)(PF₆)₂], 1,5-(1-methylpyrrolidium    1-yl)(1-methylpiperidinium) 1-yl) pentane dihexafluorophosphate    [PYRPIP₁₅(PF₆)_(2], 1,5)-bis (1-methylpiperidinium 1-yl) pentane    dihexafluorophosphate [DiPIP₁₅(PF₆)_(2], 1,5)-bis    (1-methylpyrrolidium 1-yl) pentane (hexafluorophosphate)    (tetrafluoroborate) [DiPYR₁₅(PF₆)(BF₄)], 1,5-(1-methylpyrrolidium    1-yl) (1-methyl-imidazolium-3-yl) pentane dihexafluorophosphate    [PYRMIM₁₅(PF₆)₂].    -   Electrolyte:        -   (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt. %            DiPYR_(IEE)(PF₆)₂,        -   (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %            PYRPIP₁₅(PF₆)₂,        -   (c) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %            DiPIP₁₅(PF₆)₂,        -   (d) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt. %            DiPYR₁₅(PF₆)(BF₄),        -   (e) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %            PYRMIM₁₅(PF₆)₂.        -   With reference to FIGS. 11A to 14B, the LSV test shows that            the maximum oxidation potentials of the above four ionic            liquids in the initial cycle are 4.774V, 4.929V, 4.895V and            greater than 5.0V, respectively which indicates that the            alkyl functional group Y, heterocyclic aromatic cation X₁            and X₂, and anion Z₁ and Z₂ can change the maximum oxidation            potential of the electrolyte. Among them, the electrolyte            with DiPYR₁₅(PF₆)(BF₄) added has the best ability of            withstanding high voltage. In addition, by replacing the            cations X₁ and X₂ with methylimidazole (MIM) and morpholine            (MPE) cations with result in extremely unstable            electrolytes, and the highest oxidation potential of that            cannot be determined. For the other types of ionic liquids            with two-core cationic chain and the aromatic bonded to            cation, the maximum oxidation potential of their            electrolytes at the LSV test are shown in FIG. 15/Table 7            and FIG. 16/Table 8.        -   With reference to FIGS. 15A, 15B and 15C, the maximum            oxidation potential must be greater than 4.7V to be            considered to present an improvement. Any added amount of            ionic liquid (as detailed below) would be of an amount of            10-15 wt. % in the organic electrolyte:        -   The maximum oxidation potential (V) of an organic            electrolyte, 1M LiPF6+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC, as            a control sample is 4.652V.        -   The maximum oxidation potential (V) of DiPYR₁₄(PF₆)₂, X₁ is            NMPD, X₂ is NMPD, Y is Butane, C4, Z₁ is PF₆, Z₂ is PF₆ is            4.906V.        -   The maximum oxidation potential (V) of DiPYR₁₅(PF₆)₂, X₁ is            NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.922V.        -   The maximum oxidation potential (V) of DiPYR₁₆(PF₆)₂, X₁ is            NMPD, X₂ is NMPD, Y is Hexane, C6, Z₁ is PF₆, Z₂ is PF₆ is            4.872V.        -   The maximum oxidation potential (V) of DiPYR₁₈(PF₆)₂, X₁ is            NMPD, X₂ is NMPD, Y is Octane, C8, Z₁ is PF₆, Z₂ is PF₆ is            >5.0V.        -   The maximum oxidation potential (V) of DiPIP₁₅(PF₆)₂, X₁ is            MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.895V.        -   The maximum oxidation potential (V) of DiPIP₁₈(PF₆)₂, X₁ is            MPIP, X₂ is MPIP, Y is Octane, C8, Z₁ is PF₆, Z₂ is PF₆ is            4.963V.        -   The maximum oxidation potential (V) of DiPYR₁₅(PF₆)(BF₄), X₁            is NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is PF₆, Z₂ is BF₄            is >5.0V.        -   The maximum oxidation potential (V) of DiPYR₁₅(PF₆)(BF₄), X₁            is NMPD, X₂ is NMPD, Y is Octane, C8, Z₁ is PF₆, Z₂ is BF₄            is >5.0V.        -   The maximum oxidation potential (V) of DiPIP₁₅(PF₆)(BF₄), X₁            is MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is BF₄            is 4.955V.        -   The maximum oxidation potential (V) of DiPIP₁₈(PF₆)(BF₄), X₁            is MPIP, X₂ is MPIP, Y is Octane, C8, Z₁ is PF₆, Z₂ is BF₄            is >5.0V.        -   The maximum oxidation potential (V) of PYRPIP₁₅(PF₆)₂, X₁ is            NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.929V.        -   The maximum oxidation potential (V) of PYRTEA₁₅(PF₆)₂, X₁ is            NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            >5.0V.        -   The maximum oxidation potential (V) of PYRMPE₁₅(PF₆)₂, X₁ is            NMPD, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.653V.        -   The maximum oxidation potential (V) of PYRMIM₁₅(PF₆)₂, X₁ is            NMPD, X₂ is MIM, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            unavailable.        -   The maximum oxidation potential (V) of PYRPYO₁₅(PF₆)₂, X₁ is            NMPD, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.782V.        -   The maximum oxidation potential (V) of PIPTEA₁₅(PF₆)₂, X₁ is            MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.968V.        -   The maximum oxidation potential (V) of PIPMPE₁₅(PF₆)₂, X₁ is            MPIP, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.372V.        -   The maximum oxidation potential (V) of PIPMIM₁₅(PF₆)₂, X₁ is            MPIP, X₂ is MIM, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            unavailable.        -   The maximum oxidation potential (V) of PIPPYO₁₅(PF₆)₂, X₁ is            MPIP, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.739V.        -   The maximum oxidation potential (V) of TEAMPE₁₅(PF₆)₂, X₁ is            TEA, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.562V.        -   The maximum oxidation potential (V) of TEAMIM₁₅(PF₆)₂ X₁ is            TEA, X₂ is MIM, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            unavailable.        -   The maximum oxidation potential (V) of TEAPYO₁₅(PF₆)₂, X₁ is            TEA, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            4.809V.        -   The maximum oxidation potential (V) of MIMMPE₁₅(PF₆)₂, X₁ is            MIM, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            unavailable.        -   The maximum oxidation potential (V) of MIMPYO₁₅(PF₆)₂, X₁ is            MIM, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is            unavailable.        -   The maximum oxidation potential (V) of PYRPIP₁₅(PF₆)(PF₄),            X₁ is NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is            BF₄ is >5.0V.        -   The maximum oxidation potential (V) of PYRTEA₁₅(PF₆)(PF₄),            X₁ is NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is            BF₄ is >5.0V.        -   The maximum oxidation potential (V) of PYRPYO₁₅(PF₆)(PF₄),            X₁ is NMPD, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is            BF₄ is 4.833V.        -   The maximum oxidation potential (V) of PIPTEA₁₅(PF₆)(PF₄),            X₁ is MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is            BF₄ is 4.928V.        -   The maximum oxidation potential (V) of PIPPYO₁₅(PF₆)(PF₄),            X₁ is MPIP, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is            BF₄ is 4.760V.        -   The maximum oxidation potential (V) of TEAPYO₁₅(PF₆)(PF₄),            X₁ is TEA, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is BF₄            is 4.858V.        -   The maximum oxidation potential (V) of DiPYR₁₅(TFSI)(FSI),            X₁ is NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is TFSI, Z₂ is            FSI is 4.937V.        -   The maximum oxidation potential (V) of DiPIP₁₅(TFSI)(FSI),            X₁ is MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is TFSI, Z₂ is            FSI is 4.912V.        -   The maximum oxidation potential (V) of PYRPIP₁₅(TFSI)(FSI),            X₁ is NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is TFSI, Z₂ is            FSI is 4.938V.        -   The maximum oxidation potential (V) of PYRTEA₁₅(TFSI)(FSI),            X₁ is NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is TFSI, Z₂ is            FSI is >5.0V.        -   The maximum oxidation potential (V) of PIPTEA₁₅(TFSI)(FSI),            X₁ is MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is TFSI, Z₂ is            FSI is 4.953V.        -   The maximum oxidation potential (V) of            DiPYR₁₅(CF₃BF₃)(POF₂), X₁ is NMPD, X₂ is NMPD, Y is Pentane,            C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is >5.0V.        -   The maximum oxidation potential (V) of            DiPIP₁₅(CF₃BF₃)(POF₂), X₁ is MPIP, X₂ is MPIP, Y is Pentane,            C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is 4.935V.        -   The maximum oxidation potential (V) of            PYRPIP₁₅(CF₃BF₃)(POF₂), X₁ is NMPD, X₂ is MPIP, Y is            Pentane, C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is >5.0V.        -   The maximum oxidation potential (V) of            PYRTEA₁₅(CF₃BF₃)(POF₂), X₁ is NMPD, X₂ is TEA, Y is Pentane,            C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is >5.0V.        -   The maximum oxidation potential (V) of            PIPTEA₁₅(CF₃BF₃)(POF₂), X₁ is MPIP, X₂ is TEA, Y is Pentane,            C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is 4.976V.        -   The maximum oxidation potential (V) of DiPYR₁₄(BF₄)(FSI), X₁            is NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is BF₄, Z₂ is FSI            is 4.962V.        -   The maximum oxidation potential (V) of DiPIP₁₅(BF₄)(FSI), X₁            is MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is BF₄, Z₂ is FSI            is 4.907V.        -   The maximum oxidation potential (V) of PYRPIP₁₅(BF₄)(FSI),            X₁ is NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is BF₄, Z₂ is            FSI is >5.0V.        -   The maximum oxidation potential (V) of PYRTEA₁₅(BF₄)(FSI),            X₁ is NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is BF₄, Z₂ is            FSI is >5.0V.        -   The maximum oxidation potential (V) of PIPTEA₁₅(BF₄)(FSI),            X₁ is MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is BF₄, Z₂ is            FSI is 4.974V.        -   The maximum oxidation potential (V) of DiPYR_(IEE)(PF₆)₂, X₁            is NMPD, X₂ is NMPD, Y is iethyl ether, Z₁ is PF₆, Z₂ is PF₆            is 4.774V.        -   The maximum oxidation potential (V) of DiPYR_(IEC)(PF₆)₂, X₁            is NMPD, X₂ is NMPD, Y is Diethyl carbonate, C4, Z₁ is PF₆,            Z₂ is PF₆ is 4.825V.        -   The maximum oxidation potential (V) of DiPYR_(IPO)(PF₆)₂, X₁            is NMPD, X₂ is NMPD, Y is Pentan-3-one, Z₁ is PF₆, Z₂ is PF₆            is 4.833V.        -   The maximum oxidation potential (V) of DiPYR_(IEB)(PF₆)₂, X₁            is NMPD, X₂ is NMPD, Y is Diethyl butanedioate, Z₁ is PF₆,            Z₂ is PF₆ is 4.706V.        -   With reference to FIGS. 16A and 16B, again, the maximum            oxidation potential must be greater than 4.7V to be            considered to present an improvement. Any added amount of            ionic liquid (as detailed below) would be of an amount of            1-10 wt. % in the organic electrolyte:        -   The maximum oxidation potential (V) of an organic            electrolyte, 1M LiPF6+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC, as            a control sample is 4.652V.        -   The maximum oxidation potential (V) of PYR_(1BEE)PF₆ with X₁            is NMPD, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is 4.739V.        -   The maximum oxidation potential (V) of PYR_(1BBE)PF₆ with X₁            is NMPD, Y & W are Benzyl butyl ether, Z₁ is PF₆, is 4.757V.        -   The maximum oxidation potential (V) of PYR_(1BZO)PF₆ with X₁            is NMPD, Y & W are Benzoyl, Z₁ is PF₆, is 4.746V.        -   The maximum oxidation potential (V) of PYR_(1PHC)PF₆ with X₁            is NMPD, Y & W are Phenacyl, Z₁ is PF₆, is 4.773V.        -   The maximum oxidation potential (V) of PYR_(1FRA)PF₆ with X₁            is NMPD, Y & W are 2-Furan, Z₁ is PF₆, is 4.722V.        -   The maximum oxidation potential (V) of PYR_(14FRA)PF₆ with            X₁ is NMPD, Y & W are 2-ButylFuran, Z₁ is PF₆, is 4.736V.        -   The maximum oxidation potential (V) of PYR_(1FRO)PF₆ with X₁            is NMPD, Y & W are 2-Furoyl, Z₁ is PF₆, is 4.829V.        -   The maximum oxidation potential (V) of PYR_(1BSF)PF₆ with X₁            is NMPD, Y & W are Benzenesulfonyl, Z₁ is PF₆, is 4.817V.        -   The maximum oxidation potential (V) of PYR_(1TSF)PF₆ with X₁            is NMPD, Y & W are p-Toluenesulfonyl, Z₁ is PF₆, is 4.801V.        -   The maximum oxidation potential (V) of PIP_(1BEE)PF₆ with X₁            is MPIP, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is 4.536V.        -   The maximum oxidation potential (V) of PIP_(14FRA)PF₆ with            X₁ is MPIP, Y & W are 2-ButylFuran, Z₁ is PF₆, is 4.622V.        -   The maximum oxidation potential (V) of PIP_(1FRO)PF₆ with X₁            is MPIP, Y & W are 2-Furoyl, Z₁ is PF₆, is 4.729V.        -   The maximum oxidation potential (V) of TEA_(1BEE)PF₆ with X₁            is TEA, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is 4.389V.        -   The maximum oxidation potential (V) of TEA_(14FRA)PF₆ with            X₁ is TEA, Y & W are 2-ButylFuran, Z₁ is PF₆, is 4.443V.        -   The maximum oxidation potential (V) of TEA_(1FRO)PF₆ with X₁            is TEA, Y & W are 2-Furoyl, Z₁ is PF₆, is 4.738V.        -   The maximum oxidation potential (V) of MIM_(1BEE)PF₆ with X₁            is MIM, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is            unavailable.        -   The maximum oxidation potential (V) of MIM_(14FRA)PF₆ with            X₁ is MIM, Y & W are 2-ButylFuran, Z₁ is PF₆, is            unavailable.        -   The maximum oxidation potential (V) of MIM_(14FRO)PF₆ with            X₁ is MIM, Y & W are 2-Furoyl, Z₁ is PF₆, is unavailable.        -   The maximum oxidation potential (V) of MPE_(1FRO)PF₆ with X₁            is MPE, Y & W are 2-Furoyl, Z₁ is PF₆, is unavailable.        -   The maximum oxidation potential (V) of PYO_(1FRO)PF₆ with X₁            is PYO, Y & W are 2-Furoyl, Z₁ is PF₆, is unavailable.        -   The maximum oxidation potential (V) of PYO_(1FRO)BF₄ with X₁            is NMPD, Y & W are 2-Furoyl, Z₁ is BF₄, is 4.926V.        -   The maximum oxidation potential (V) of PYR_(1FRO)FSI with X₁            is NMPD, Y & W are 2-Furoyl, Z₁ is FSI, is 4.877V.        -   The maximum oxidation potential (V) of PYR_(1FRO)TFSI with            X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is TFSI, is 4.917V.        -   The maximum oxidation potential (V) of PYR_(1FRO)CF₃BF₃ with            X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is CF₃BF₃, is 4.958V.        -   The maximum oxidation potential (V) of PYR_(1FRO)POF₂ with            X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is POF₂, is 4.923V.        -   The maximum oxidation potential (V) of PYR_(1FRO)MeSO₄ with            X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is MeSO₄, is 4.607V.

With reference to Tables 7 and 8, the LSV test shows that the highestoxidation potential of the related electrolyte cannot be determined,when the cation X₁ and X₂ of two-core cationic chain ionic liquid aremethylimidazole (MIM) and morpholine (MPE) cations. There is no obviousimprovement on the ability of withstanding high voltage. In addition,while the cation X₁ of ionic liquid with aromatic bonded to cation isthe N-methyl pyrrolidine (NMPD), the maximum oxidation potential ofrelated electrolyte is higher than 4.7 V, which shows an enhancement onthe withstanding high voltage of electrolyte.

Embodiment 4

According to the maximum solubility, an ionic liquid with the two-corecationic chain or an ionic liquid with aromatic bonded to cation isadded to a non-aqueous electrolyte. The amount of ionic liquid is about10-15 wt. % of the electrolyte. Then, a cyclic voltammetry (CV) isconducted using the AutoLab 302N electrochemistry instrument tounderstand the oxidation-reduction reaction between the electrolyte andthe graphite anode under different voltages.

CV Test Conditions:

Working electrode: (Anode material) meso carbon micro bead

-   -   MCMB:SuperP:CMC:SBR=95.5:1.0:1.5:2.0

Reference electrode Li, counter electrode Li, scan voltage range 0˜2.5V,scan rate 1 mV/s.

-   1. Traditional cationic ionic liquid with aromatic heterocycle:    1-propyl-1-methylpyrrolidium hexafluorophosphate (PYR₁₃PF₆)    -   Electrolyte: 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt.        % PYR₁₃PF₆        -   With reference to FIG. 17, the CV test shows that a            reduction peak appeared at 0.7-1.0 V when 15 wt. % PYR₁₃PF₆            ionic liquid was added to the electrolyte. The reason being            that the PYR₁₃ ⁺ cations are intercalated into the layered            structure on the surface of MCMB, preventing lithium ions            from migrating into the layered structure. This leads to the            generation of lithium precipitation on the surface of anode,            thereby increasing the interface impedance, and causing a            decline in the cycle stability of battery.-   2. Two-core cationic chain ionic liquid: 1,5 Bis(1-methylpyrrolidium    1-yl) pentane dihexafluorophosphate [DiPYR₁₅(PF₆)₂], 1,8    Bis(1-methylpyrrolidium 1-yl) octane dihexafluorophosphate    [DiPYR₁₈(PF₆)₂]    -   Electrolyte: (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10        wt. % DiPYR₁₅(PF₆)₂, (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt.        % VC+10 wt. % DiPYR₁₈(PF₆)₂        -   With reference to FIGS. 18A and 18B, there was no reduction            peak at 0.7-1.0 V when 10 wt. % of DiPYR₁₅(PF₆)₂ or 10 wt. %            of DiPYR₁₈(PF₆)₂ ionic liquid is added to the electrolyte.            This indicates that when the molecular weight and functional            group of the cation is sufficiently large, the ionic liquid            would not be able to intercalate into the MCMB layered            structure. The ionic liquids with two-core cationic chain or            the cation ionic liquid with aromatic bonded to the cation            according to the invention, in which the two cations are            linked together, their molecular weight is increased            sufficiently so as to result in poor intercalation into the            anode material.-   3. Replacement of the alkyl chain Y with other functional groups,    and replacement of the cation X₁ and X₂ with other heterocyclic    aromatic or amine, and replacement of other anionic groups Z₁ and    Z₂: Taking the following two ionic liquids with dual core cationic    chain as examples: bis[2-(1-methylpyrrolidinium 1-yl) ethyl] ether    dihexafluorophosphate [DiPYR_(IEE)(PF₆)₂], 1,5-(1-methylpyrrolidium    1-yl)(1-methylpiperidinium 1-yl) pentane dihexafluorophosphate    [PYRPIP₁₅ (PF₆)_(2], 1,5)-bis(1-methylpiperidinium 1-yl) pentane    dihexafluorophosphate [DiPIP₁₅(PF₆)₂], 1,5-bis(1-methylpyrrolidium    1-yl) pentane (hexafluorophosphate) (tetrafluoroborate)    [DiPYR₁₅(PF₆)(BF₄)]    -   Electrolyte: (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15        wt. % DiPYR_(IEE)(PF₆)₂, (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1        wt. % VC+10 wt. % PYRPIP₁₅(PF₆)₂, (c) 1M LiPF₆+EC:DMC:EMC=1:1:1        (vol.)+1 wt. % VC+10 wt. % DiPIP₁₅(PF₆)₂, (d) 1M        LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt. %        DiPYR_(is)(PF₆)(BF₄)    -   With reference to FIGS. 19A to 19D, there is no reduction peak        at 0.7-1.0 V when DiPYR_(IEE)(PF₆)₂, DiPIPPYR₁₅(PF₆)₂,        DiPIP₁₅(PF₆)₂ or DiPYR₁₅(PF₆)(BF₄) ionic liquid is added to the        electrolyte. It indicates that the molecular weight of the        two-core structure and its functional group is sufficiently        large to minimize intercalation into the MCMB layered structure,        yet does not hinder the intercalation and exfoliation of lithium        ions. The interface impedance on the surface of the anode is        reduced.

Embodiment 5

A pouch cell battery with a capacity of 40 Ah with the ionic liquidadded to the organic electrolyte is used to verify or authenticate thecomposition and structure of a solid electrolyte interface film (SEI) onthe surface of the anode during the charging and discharging processesof the lithium ion battery with the two-core structure ionic liquidaccording to the invention developed in this patent. In the test, thebattery undergo splint formation to charge to 3.5 V, and then dischargewith a small current to 2.0 V. The battery is disassembled in an inertatmosphere glove box with the anode being removed. The removed anode issoaked in the dimethyl carbonate (DMC) for about 15 minutes, followed byshaking the anode to remove any remaining lithium salt. The anode isthen left to dry in the shade.

The National Synchrotron Radiation Research Center (NSRRC) Beamline atthe 20A1 station is used to perform Soft X-ray Absorption Spectroscopy(sXAS) to verify the composition and structure of the SEI film on thesurface of anode. The oxygen K-edge absorption spectrum includes totalelectron yield (TEY) and total fluorescence yield (TFY). In TEY, due tothe restraint of the coulomb force between electrons, it would not beeasy for the electrons deep inside the electrode to reach the electrodesurface and be received. Only the electrons close to the surface areattracted by the applied bias and are received by the receiver. As such,the structure of the material in the range of 10 nm on a surface can beanalyzed. As for the TFY, fluorescence is composed of photons, it willnot be restricted by the coulomb force. It is useful indetecting/analyzing electronic structure deeper within the electrode,i.e. in the range of 200 nm on a surface.

Synchrotron sXAS Experiment Conditions:

-   1. A pouch cell of lithium iron phosphate (LFP) battery with the    capacity of 40 Ah.-   2. Splint formation: charge at the 0.01 C for 3 hours, charge at the    0.1 C to 3.6 V, and then discharge at the 0.1 C to 2.0 V;-   3. The anode material is meso carbon micro bead    MCMB:SuperP:CMC:SBR=95.5:1.0:1.5:2.0;-   4. Electrolyte: (a) Organic electrolyte (OE): 1M    LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC, (b) 1M    LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+6 wt. % PYRTEA₁₅(PF₆)₂, (c)    1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+6 wt. %    DiPYR₁₅(PF₆)₂, (d) 1M LiPF6+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+6 wt.    % DiPYR_(IEE)(PF₆)₂;-   5. Oxygen K-edge total electron yield (TEY), Energy range: 525˜555    eV.

With reference to FIG. 20, the standard Li₂CO₃ product is tested byX-ray absorption spectrum O K-edge TEY. The characteristic peakpositions of C═O (π*bond) and C—O (α*bond) of CO₃ ²⁻ are at 533.5 eV,538.7 eV and 542 eV, respectively. A pouch cell of LFP battery with thecapacity of 40 Ah with organic electrolyte (OE) without adding any ionicliquid of the invention is charged at the 0.01 C for 3 hours, charge atthe 0.1 C to 3.6 V, and then discharged at the 0.1 C to 2.0 V, the SEIfilm produced by the reaction of interface between the electrolyte andanode is detected. The TEY test result shows that the characteristiccurve is similar to that of the standard Li₂CO₃, and an obviouscharacteristic peak appears at 533.5 eV, indicating that the structureof SEI film produced by the OE electrolyte is mainly Li₂CO₃.

Again with reference to FIG. 20, the ionic liquid with dual corestructure, including PYRTEA₁₅(PF₆)₂, DiPYR₁₅(PF₆)₂ and DiPYR_(IEE)(PF₆)₂are added at 6 wt. % to the OE electrolyte respectively. Three samplesof pouch cell LFP battery, capacity of 40 Ah is used, withOE+PYRTEA₁₅(PF₆)₂, organic electrolyte (OE)+DiPYR₁₅(PF₆)₂ andOE+DiPYR_(IEE)(PF₆)₂ respectively. The surface of the anodes is testedby the sXAS absorption spectrum O K-edge TEY. Each of them shows anobvious Li₂CO₃ characteristic peak at 533.5 eV, but the other peaks alsoappear at the position of 532˜533 eV. The main components includes thecharacteristic peaks of COH at 531.7 eV and the O—O of organic lithiumsalt ROCO₂Li at 532.5 eV, which means in each of the three samples, athin layer of organic film is formed in the range of ˜5 nm on thesurface of anode. The amount of organic film formed in the three samplesare of the order ofOE+DiPYR_(IEE)(PF₆)₂>OE+DiPYR₁₅(PF₆)₂>OE+PYRTEA₁₅(PF₆)₂. It is concludedthat the addition of the ionic liquids according to the invention notonly inhibits the intercalation at the anode, but also result in theformation of a thin layer of organic film on the anode surface. Byadding an appropriate amount of the ionic liquid to the electrolyte, theinterface resistance will be reduced and the thermal stability of theoverall lithium-ion battery will be improved as the ionic liquid hashigh melting point and is an effective flame retardant.

Embodiment 6

The performance of LFP batteries with the pouch cell of 40 Ah and 60 Ahwith different electrolyte formulations.

Preparation of Cathode Sheet

Cathode active material: LFP, binder: polyvinylidene fluoride (PVDF),conductive agent: carbon black (Super P®) are mixed according to theweight ratio of LFP:Super P:PVDF=96:2:2, followed by adding the solvent:N-methyl pyrrolidone. It is then stirred and dispersed uniformly in avacuum stirring machine to obtain the cathode slurry. The cathode slurryis uniformly coated on an aluminum foil by a coating machine, and thesolvent is removed by the drying in hot air. The cathode sheet isobtained by cold pressing and slitting.

Preparation of Anode Sheet

Anode active material: meso carbon micro bead (MCMB), conductive agent:carbon black (Super P), thickener: sodium carboxymethyl cellulose (CMC),binder: styrene butadiene rubber (SBR) emulsion are mixed in a ratio ofMCMB:Super P:CMC:SBR=95.5:1.0:1.5:2.0 with deionized water as solvent.It is stirred and dispersed uniformly in a vacuum stirring machine toobtain the anode slurry. The anode slurry is uniformly coated on thecopper foil by a coating machine, and the solvent is removed by thedrying in hot air. Anode sheet is obtained by cold pressing andslitting.

Preparation of Electrolyte

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 mole/L (M) of LiPF₆ in the specified sequence. Theelectrolyte is formed after mixing. Electrolyte with differentfilm-forming agent (A), stabilizer (B), ionic liquid (C) are shown inFIG. 21A, FIG. 21B and Table 9.

With Reference to FIG. 21A, Electrolyte Formula 1:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A) and 1 M of LiPF₆ inthe specified sequence. Film-forming agent (A): VC: Vinylene carbonateat 1 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 2:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A) and 1 M of LiPF₆ inthe specified sequence. Film-forming agent (A) is VC: Vinylene carbonateat 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %. The electrolyteis formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 3:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B) and 1M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC:Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt.%, the stabilizer (B) is EPFCP: Ethoxy(pentafluoro)cyclotriphosphazeneat 3 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 4:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), ionic liquid (C) and1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC:Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt.%, the ionic liquid (C) is PYR₁₃PF₆ at 5 wt. %. The electrolyte isformed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 5:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is HFCP: Hexafluorocyclotriphosphazene at 2.9 wt. %, the ionic liquid (C) is PYR₁₃PF₆ at 5wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 6:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP:Ethoxy(pentafluoro)cyclotriphosphazene at 2.9 wt. %, the ionic liquid(C) is PYR₁₃PF₆ at 5 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 7:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP:Ethoxy(pentafluoro)cyclotriphosphazene at 2.9 wt. %, the ionic liquid(C) is PYR₁₃PF₆ at 10 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 8:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP:Ethoxy(pentafluoro)cyclotriphosphazene at 2.9 wt. %, the ionic liquid(C) is PYR₁₃PF₆ at 15 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 9:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), ionic liquid (C) and1 M of LiPF6 in the specified sequence. Film-forming agent (A) is VC:Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt.%, the stabilizer, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. Theelectrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 10:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is HFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21A, Electrolyte Formula 11:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21A, Electrolyte Formula 12:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 8 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21A, Electrolyte Formula 13:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 10 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21A, Electrolyte Formula 14:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 2 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21A, Electrolyte Formula 15:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 3 wt. % and FEC: Fluoroethylenecarbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21B, Electrolyte Formula 16:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21B, Electrolyte Formula 17:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF6 in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 3 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionicliquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed aftermixing.

With Reference to FIG. 21B, Electrolyte Formula 18:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.8 wt. %, theionic liquid (C) is Furoyl-PYR₁₁(PF₆)₂ at 6 wt. %. The electrolyte isformed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 19:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.8 wt. %, theionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formedafter mixing.

With Reference to FIG. 21B, Electrolyte Formula 20:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.8 wt. %, theionic liquid (C) is DiPYR_(IEE)(PF₆)₂ at 6 wt. %. The electrolyte isformed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 21:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.5 wt. %, theionic liquid (C) is PYRPIP_(IEE)(PF₆)₂ at 6 wt. %. The electrolyte isformed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 22:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.5 wt. %, theionic liquid (C) is DiPIP₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formedafter mixing.

With Reference to FIG. 21B, Electrolyte Formula 23:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC)and ethyl methyl carbonate (EMC) are mixed according to the weight ratioof EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organicsolvent followed by adding film-forming agent (A), stabilizer (B), ionicliquid (C) and 1 M of LiPF₆ in the specified sequence. Film-formingagent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylenecarbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.5 wt. %, theionic liquid (C) is DiPYR₁₅(PF₆)(BF₄) at 6 wt. %. The electrolyte isformed after mixing.

Formation of LFP Battery

With reference to FIGS. 22A and 22B, cathode sheet, anode sheet, andseparator are laminated. Ultrasonic welding is used to attach theconductive lugs to obtain a bare battery cell. The bare battery cell isinserted into the aluminum-plastic film pit. After encapsulation, anyone of the electrolytes 1 to 23 as detailed in FIG. 21/Table 9 isinjected. The pouch is sealed. The pouch battery is allowed to stand,undergo cold pressing, formation, exhausting, capacity testing, agingand other processes, the pouch cell of LFP battery with the capacity of40˜60 Ah is obtained. The specification of battery is shown in thefigure below.

Self-extinguishing time SET of electrolyte for battery preparedaccording to FIG. 21/Table 9

1.2 g of each electrolyte as detailed in FIG. 21/Table 9 is placed ontoa glass fiber filter with a diameter of 47 mm and a thickness of 0.5 mm.The electrolyte is ignited and burnt. The time from ignition toextinguishment per gram of electrolyte in each of the batteries in FIG.21/Table 9 is recorded, the unit is sec/g, referred to as theself-extinguishing time (Self-extinguish time, SET). Each of Electrolyteformula 1 to 23 are tested respectively. The results are produced inFIG. 10.

Performance Test of Lithium-Ion Battery Prepared According to FIG.21/Table 9

At 25° C., each LFP battery with any one of electrolyte 1 to 23 ischarged to 3.6 V at a constant current of 0.5 C followed by charging thebattery at a constant voltage of 3.6 V until the current drops to 0.05C, and then discharged to 2.5 V at a constant current of 0.5 C. This isone charge-discharge cycle and this is the first discharge capacity oflithium-ion battery. Under the aforementioned charge and dischargeconditions, the lithium-ion battery is subjected to multiple cycles oftesting until the discharge capacity reaches 80% of the first dischargecapacity (The capacity retention (C.R.) being 80%). The number of chargeand discharge cycles until C.R.=80% of respective batteries is recorded.The results are produced in FIG. 10. The lithium ion battery withdifferent electrolyte formula (1 to 23) are tested respectively.

Internal Impedance Test

The internal impedance AC IR value of the lithium ion battery with anyone of electrolyte formula 1 to 23 as detailed in Table 9 is detected byHIOKI BT3561 battery internal resistance meter and the results arerecorded in FIG. 10.

Referring to FIGS. 23A and 23B, it shows the performance of LFP batteryin the form of pouch cell 40 Ah (No. 1 to 8) and the performance of LFPbattery in the form of pouch cell 60 Ah (No. 9 to 23).

The self-extinguishing time, internal impedance and performance of eachbattery with any one of the electrolyte formulae listed in FIG. 23 arerecorded in FIG. 10. The batteries are given the same number (No.) asthe number of assigned to each electrolyte formulae as detailed in FIG.23.

With reference to FIG. 23A, No. 1, the LFP battery 40 Ah withelectrolyte formula 1 has a self-extinguishing time of 63 sec/g, aninternal impedance ACIR (Alternate Current Internal Resistance) of 3.27mΩ and the charge/discharge cycle number under 25 degree C. is 1359.

In No. 2, the LFP battery 40 Ah with electrolyte formula 2 has aself-extinguishing time of 58 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.05 mΩ and thecharge/discharge cycle number under 25 degree C. is 1492.

In No. 3, the LFP battery 40 Ah with electrolyte formula 3 has aself-extinguishing time of 45 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.92 mΩ and thecharge/discharge cycle number under 25 degree C. is 1553.

In No. 4, the LFP battery 40 Ah with electrolyte formula 4 has aself-extinguishing time of 36 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.48 mΩ and thecharge/discharge cycle number under 25 degree C. is 1265.

In No. 5, the LFP battery 40 Ah with electrolyte formula 5 has aself-extinguishing time of 22 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.12 mΩ and thecharge/discharge cycle number under 25 degree C. is 1463.

In No. 6, the LFP battery 40 Ah with electrolyte formula 6 has aself-extinguishing time of 18 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.86 mΩ and thecharge/discharge cycle number under 25 degree C. is 1620.

In No. 7, the LFP battery 40 Ah with electrolyte formula 7 has aself-extinguishing time of 8 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.28 inn and thecharge/discharge cycle number under 25 degree C. is 1335.

In No. 8, the LFP battery 40 Ah with electrolyte formula 8 has aself-extinguishing time of 3 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 4.37 mΩ and thecharge/discharge cycle number under 25 degree C. is 1065.

In No. 9, the LFP battery 60 Ah with electrolyte formula 9 has aself-extinguishing time of 27 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.05 mΩ and thecharge/discharge cycle number under 25 degree C. is 1517.

In No. 10, the LFP battery 60 Ah with electrolyte formula 10 has aself-extinguishing time of 17 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.56 mΩ and thecharge/discharge cycle number under 25 degree C. is 1662.

In No. 11, the LFP battery 60 Ah with electrolyte formula 11 has aself-extinguishing time of 11 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.37 mΩ and thecharge/discharge cycle number under 25 degree C. is 1918.

In No. 12, the LFP battery 60 Ah with electrolyte formula 12 has aself-extinguishing time of 8 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.69 mΩ and thecharge/discharge cycle number under 25 degree C. is 1739.

In No. 13, the LFP battery 60 Ah with electrolyte formula 13 has aself-extinguishing time of 6 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.05 mΩ and thecharge/discharge cycle number under 25 degree C. is 1505.

In No. 14, the LFP battery 60 Ah with electrolyte formula 14 has aself-extinguishing time of 14 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 3.18 mΩ and thecharge/discharge cycle number under 25 degree C. is 1554.

In No. 15, the LFP battery 60 Ah with electrolyte formula 15 has aself-extinguishing time of 13 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 4.06 mΩ and thecharge/discharge cycle number under 25 degree C. is 1258.

In No. 16, the LFP battery 60 Ah with electrolyte formula 16 has aself-extinguishing time of 10 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.32 mΩ and thecharge/discharge cycle number under 25 degree C. is 2035.

In No. 17, the LFP battery 60 Ah with electrolyte formula 17 has aself-extinguishing time of 8 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.45 mΩ and thecharge/discharge cycle number under 25 degree C. is 1906.

In No. 18, the LFP battery 60 Ah with electrolyte formula 18 has aself-extinguishing time of 14 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.63 mΩ and thecharge/discharge cycle number under 25 degree C. is 1734.

In No. 19, the LFP battery 60 Ah with electrolyte formula 19 has aself-extinguishing time of 10 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.39 mΩ and thecharge/discharge cycle number under 25 degree C. is 1895.

In No. 20, the LFP battery 60 Ah with electrolyte formula 20 has aself-extinguishing time of 11 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.15 mΩ and thecharge/discharge cycle number under 25 degree C. is 2120.

In No. 21, the LFP battery 60 Ah with electrolyte formula 21 has aself-extinguishing time of 12 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.46 mΩ and thecharge/discharge cycle number under 25 degree C. is 1887.

In No. 22, the LFP battery 60 Ah with electrolyte formula 22 has aself-extinguishing time of 13 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.43 mΩ and thecharge/discharge cycle number under 25 degree C. is 1864.

In No. 23, the LFP battery 60 Ah with electrolyte formula 23 has aself-extinguishing time of 9 sec/g, an internal impedance ACIR(Alternate Current Internal Resistance) of 2.23 mΩ and thecharge/discharge cycle number under 25 degree C. is 2117.

With reference to the batteries 1 to 3 in Table 10/FIG. 23A: the organicelectrolyte contains 1% VC (Battery 1), which is considered as flammableelectrolyte. The self-extinguishing time is 63 sec/g, and the internalimpedance of the battery is 3.27 mΩ. The number of charge-dischargecycle is only 1359 cycles at the 0.5 C until reaching the capacityretention (C.R.) of 80%. By adding 1% FEC (Battery 2) and 3% EPFCP(Battery 3) in sequence, the self-extinguishing time is significantlyreduced, and the long-cyclic performance of the battery tends to beslightly improved.

For Batteries 4 to 6 in FIG. 10/FIG. 23A: 1% VC, 1% FEC, and then 5%PYR₁₃PF₆ are added to the organic electrolyte (Battery 4), theself-extinguishing time is significantly reduced compared with that ofBattery 2. By adding a high melting point, low vapor pressure ionicliquid in the electrolyte, the self-extinction ability will besignificantly improved but the performance of the overall battery drops.This is because PYR₁₃PF₆ ionic liquid is used and PF₆ ⁻ readilyintercalate into the layered structure of graphite, resulting in asignificant increase in the internal resistance of the relevantlithium-ion battery. In the Battery 5 2.9% HFCP is added as Stabilizerand in Battery 6 2.9% EPFCP is added as stabilizer. Theself-extinguishing times of Batteries 5 and 6 are significantly reducedwhen comparing to Battery 4. The performance of the Batteries 5 and 6have improved when comparing to Battery 4. Based on the test results,the addition of EPFCP as a stabilizer produce better results.

The Batteries 9 to 11 in FIG. 23A may be considered similar to Batteries4 to 6 in FIG. 23A. By using DiPYR₁₅(PF₆)₂ as the ionic liquid with 2%HFCP or 2% EPFCP added as stabilizers, the self-extinguishing times ofboth are significantly reduced, and the performance of the Batterieshave been enhanced. The use of EPFCP as a stabilizer produce betterresults.

For Batteries 6 to 8 om FIG. 23A, the organic electrolyte is fixed with1% VC, 1% FEC as the film forming agents and 2.9% EPFCP, 5, 10, 15%PYR₁₃PF₆ respectively, or 6, 8, 10% DiPYR₁₅(PF₆)₂ respectively forBatteries 11 to 13. The self-extinguishing time for these batteriesreduces by increasing the amount of ionic liquid added. However, theimpedance value of battery increases with the amount of ionic liquidadded resulting in overall battery performance. Therefore, it isimportant to find the optimal amount of A+B+C and it is a fine balance.

As to Batteries 11, 14 to 15 in FIG. 23A, it shows that the increase inthe amount of film-forming agent VC will significantly increase thebattery impedance, resulting in the poor performance.

With reference to Batteries 11 and 16 to 17 in FIG. 23A, by increasingthe FEC content as the film forming agent, the self-extinguishing timeis slightly reduced while the impedance value of battery remainsrelatively stable without significant increment. Among them, Battery 16with 2% FEC as the film-forming agent shows best stability.

Batteries 16 in FIG. 23A, 18 to 23 in FIG. 23B show the bestperformance, with 1% VC, 2% FEC, 2.5˜2.8% EPFCP and 6% ionic liquidadded to the organic electrolyte, with ionic liquid being a dual-corecationic chain or the aromatic bonded to cation according to theinvention. Among them, the range of self-extinguishing time is from 9 to14 sec/g, which is considered as a flame-retardant electrolyte. Byadding an appropriate amounts of stabilizer and ionic liquid, a uniformand dense of SEI film with low impedance can be formed on the surface ofthe anodes which effectively reduce the internal impedance of battery toabout 2.15˜2.46 mΩ, consequently enhance the performance of the overallbatteries.

1. An ionic liquid for adding to an electrolyte of a lithium-ionbattery, wherein the ionic liquid comprises a compound with a dual corestructure having the general formula (I):Z₁X₁YX₂Z₂  (formula I), wherein Z₁ and Z₂ are selected from the groupconsisting of PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻ (difluorophosphate),BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻, bis(oxalato) borate),BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻(trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl sulfate)and

wherein X₁YX₂ is selected from the group consisting of

1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane

1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane

Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate

1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one and

Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate; and wherein anoverall amount of ionic liquid added to the electrolyte is 0.1-15 wt. %.2-11. (canceled)
 12. An ionic liquid for adding to an electrolyte of alithium-ion battery, the ionic liquid comprises a compound with a dualcore structure having the general formula (I):

wherein each of cationic group X₁ and X₂ are heterocyclic aromatic andamine.
 13. The ionic liquid as claimed in claim 12, wherein theheterocyclic aromatic is selected from a group consisting piperidinium,pyrrolidinium, pyrazolium and pyridinium.
 14. The ionic liquid asclaimed in claim 12, wherein the amine is selected from a groupconsisting quaternary ammonium, azepane and phosphonium.
 15. The ionicliquid as claimed in claim 12, wherein Y is any one of C3˜C10 alkylgroup.
 16. The ionic liquid as claimed in claim 12, wherein Y isselected from a group consisting of sulfonyl, carbonic acid, ether,ketone group and ester.
 17. The ionic liquid as claimed in claim 12,wherein X₁YW is selected from a group consisting:

Benzyl-2-(1-methylpyrrolidinium 1-yl) ethyl ether

Benzyl-4-(1-methylpyrrolidinium 1-yl) butyl ether

1-(1-Benzoyl)-1-methyl pyrrolidinium

1-(2-Phenacyl)-1-methyl pyrrolidinium

1-(Furan 2-yl)-1-methyl pyrrolidinium

1-(butyl furan 2-yl)-1-methyl pyrrolidinium

1-(2-Furoyl)-1-methyl pyrrolidinium

1-Benzensulfonyl-1-methyl pyrrolidinium

1-p-Toluenesulfonyl-1-methyl pyrrolidinium.
 18. (canceled)
 19. A lithiumion battery comprising a positive electrode, a negative electrode, aseparator, an electrolyte and one or more ionic liquid as claimed inclaim
 1. 20. The lithium ion battery as claimed in claim 19 furthercomprising a stabilizer, wherein the stabilizer is a cyclophosphazenecompound.
 21. The lithium ion battery as claimed in claim 20, whereinthe stabilizer is selected from the group consisting of:

Hexafluoro cyclotriphosphazene; and

Ethoxy (pentafluoro) cyclotriphosphazene.
 22. The lithium ion battery asclaimed in claim 20, wherein an amount of the stabilizer added to theelectrolyte is 0.1-2.9 wt. %.
 23. The lithium ion battery as claimed inclaim 19, wherein a SEI film forming agent is added to the electrolyte.24. The lithium ion battery as claimed in claim 23, wherein the SEI filmforming agent is selected from the group consisting of fluoroethylenecarbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate(VEC), ethylene sulfite (ES), propylene sulfite (PS), and ethylenesulfate (DTD), and combinations thereof.
 25. The lithium ion battery asclaimed in claim 23, wherein an amount of the SEI film forming agentadded to the electrolyte is 0.1-5 wt. %.
 26. The lithium ion battery asclaimed in claim 19, wherein the electrolyte is a non-aqueouselectrolyte; wherein optionally, the non-aqueous electrolyte comprises alithium salt selected from the group consisting of LiPF₆, LiClO₄, LiBF₄,LiSO₃CF₃, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂CF₂CF₃)₂, LiAsF₆, LiAlCl₄,LiNO₃, LiPOF₂, LiB(C₂O₄)₂, LiBF₂(C₂O₄), LiCF₃BF₃, and combinationsthereof; and wherein optionally, a concentration of the lithium salt inthe electrolyte is 0.5˜1.5 mol/L.
 27. The lithium ion battery as claimedin claim 26, wherein the nonauqeous electrolyte comprises an organicsolvent selected from the group consisting of carbonate, carboxylate,ether, ketone, and combinations thereof; wherein optionally, thecarbonate is selected from the group consisting of ethylene carbonate(EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethylcarbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate, dibutylcarbonate, and a combination thereof; wherein optionally, thecarboxylate is carboxylic acid ester; wherein optionally, the carboxylicacid ester comprises at least one of methyl acetate, ethyl acetate,methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate andpropyl acetate, and a combination thereof; and wherein optionally, thepositive electrode comprises an active material which is a lithium metalcomplex oxide compound.
 28. The lithium ion battery as claimed in claim27, wherein a metal element of the lithium metal complex oxide isselected from the group consisting of a transition metal and anon-transition metal; wherein optionally, the transition metal isselected from the group consisting of vanadium, titanium, chromium,copper, iron, nickel and cobalt; and wherein optionally, thenon-transition metal is selected from the group consisting of aluminumand manganese.
 29. The lithium ion battery as claimed in claim 19,wherein the negative electrode comprises an active material selectedfrom the group consisting of soft carbon, hard carbon, artificialgraphite, natural graphite, meso carbon micro bead (MCMB), silicon,silicon oxide compounds, silicon carbon composites, lithium titanateoxide, and metals that form alloys with lithium; wherein optionally, thenegative electrode comprises an active material that is carbon-based,silicon-based or tin-based; wherein optionally, the separator comprisesa membrane; and wherein optionally, the membrane comprises a materialselected from the group consisting of polyethylene (PE), polypropylene(PP), polyvinylidene fluoride (PVDF), ceramic material, glass fiber andcombinations thereof.